“Letters About Geology,” by “Professor Pickaxe” (from The Student, May 1853; pp. 7-9)
THE EARTH’S CRUST.
My Young Friends:
Most of you, no doubt, are acquainted with the outlines of Geography, which treats of the oceans, continents, mountans, valleys, and other divisions of the surface of the earth. After gaining the knowledge of these interesting things, many of you have doubtless also thought that you would like to know something more of those deeper mysteries which are generally hidden under the earth’s surface, and of which the science of Geology treats. I am now going to tell you about some of these things; and in doing this, I will try to use language so plain that all of you can understand me.
Come along with me, then, in imagination, down to that meadow yonder, where the ground is often covered with water, owing either to a freshet in the river, or to the rushing down of streams from the hills during heavy rains. Now, suppose we should commence here and dig down for thousands and thousands of feet, and through the whole crust of the earth (all the parts of which we will suppose to be complete in this place), what do you think we would find as we proceed downard?
For the first few inches or feet—it might be ten, twenty, or even fifty feet—we should pass through layers of blackish earth. These, like all other layers of soil or rock, are, in the plural, called Strata, and any single one of them is called a Stratum. These layers, or strata, were formed there by the settlings of mud, sand, etc., from the overflowing waters, and constitute what is called Alluvium, or the Alluvial Formation—a name taken from a Latin word, which signifies the overflowing of a stream. If you look on the accompanying diagram, you will find this formation represented by the first, or uppermost, division.
Digging through this formation, we next come to a much thicker deposit of clay, sand, gravel, and small and large stones, more or less rounded. Though these deposits are for the most part dis-
tinctly stratified, that is, arranged in strata or layers, they are, nevertheless, in many places mixed confusedly together, as will be seen represented in the second division of the diagram. At almost every place where a bank is dug down, or where excavations for a cellar or a well are made, examples of this deposit may be seen. It is called the Diluvial Formation, from a Latin word which signifies a deluge, or an overflowing of the sea.
Proceeding still downward, we next come to layers of sand, clay, slate, lime, etc., more or less hardened into rock, and of a thickness estimated at from 1,300 to 2,500 feet. If our digging operations happened to be at the right place, we would probably find in these strata, petrified plants, the shells of shell-fish, and the bones of animals, most of which would be totally different from any now living. These remains of plants and animals are called Fossiles [sic], or Organic Remains. Remember that definition. These layers constitute what are called the Tertiary Formation, which you may see represented in the third division of the diagram from the top.
Passing through these deposits, we next come to strata or layers of chalk, sandstone, etc., the estimates of whose thickness have been from 600 to 1,200 feet. Or if we did not find the chalk (as would be the case if the search were made in this country), we should find a rock formed at the same time the chalk was formed elsewhere, which fact is determined by its containing the same kinds of organic remains. These strata constitute what are called the Chalk, or Cretaceous system, and are represented in the fourth division of the diagram.
We next pass through strata of a curious kind of limestone, called Oolite, or Roestone, from its resemblance to the roe of a fish; thence through another kind of limestone, called Lias, interspersed with slate and various other stones. These deposits abound with the remains of the most interesting animals, which are entirely absent from the higher deposits, and some of which we intend to describe in a future letter. The Oolite and Lias systems are represented in the fifth division of the diagram from the top, and the estimates of their thickness, taken together have ranged from 3,000 to 3,600 feet.
Passing still downward, we next descend through the New Red Sandstone system, consisting mostly of layers of that stone (sometimes called Freestone, or Brownstone) fo which the fronts of some of the better houses in New York city are built. These rocks are remarkable for their exhibiting, in some places (as in the quarries along the Connecticut River, for instance), the tracks of numerous kinds of birds, some of which were of an enormous size, commonly stepping a distance of six feet. This system of formation is represented by the sixth division of the diagram. Its thickness has been estimated variously from 900 to 1,200 feet.
Beneath the New Red Sandstone system we would come to what has been called the great Coal Formation, or the Carboniferous System. This consists of beds of slate, limestone, and various other kinds of rock, among which the coal is most deserving of notice. It is from this portion of the earth’s crust that we derive the fuel which warms us in winter, which cooks our food, drives our engines, and accomplishes so many other useful purposes. This formation is shown in the seventh division of the diagram, in which the darker seams represent the coal. The thickness of this whole group of rocks has been estimated at about 3,000 feet, or a little more than half a mile.
We should next descend through the Mountain Limestone, about 2,700 feet thick, and thence through the Old Red Sandstone, said to measure a thickness of 10,000 feet, or a little short of two miles. These formations are severally represented in the eighth and ninth divisions of the diagram. The Mountain Limestone abounds with sea shells, and the Old Red Sandstone contains the remains of a great many fishes. These fossils, in both cases, are mostly of different kinds from any of those contained in the strata above.
After this we descend through the rocks of the Silurian and Cambrian systems, so called from the districts in England where the up-tilled straits, belonging to them, appear on the surface of the ground. The
whole thickness of these groups of rocks has not been so well ascertained; but the highest estimates, made in England some years ago, give them the almost incredible thickness of 120,000 feet, or over twenty-two miles! (see the tenth division of the diagram from the top). The animals and plants which lived during the formation of these strata, were almost all such as only inhabited the ocean, and scarcely any of their kind existed while the strata above them were being formed.
We have now completed our general survey of what are called the Fossiliferous Rocks, that is, the rocks which contain the remains of plants and animals petrified, or turned into stone. Immediately under these lie the Primary Stratified, and under these the Primary Unstratified, or granite rocks. These primary rocks contain no remains or impressions of vegetable or animal forms, from which fact, as also from other considerations, it is inferred that no living beings existed upon the earth at the time they were formed.
I will tell you some very curious things about these rocks, with others, in a future letter; but I can now only say that it is generally supposed (I think conclusively proved) that the materials of the stratified rocks were originally deposited in the bottoms of oceans, lakes, or other waters which then overflowed the earth, and that they subsequently became hardened as we now find them; but that the Unstratified ones were originally like newly-ejected lava in a melted state, from heat, and that they afterward hardened by becoming cool.
We have thus passed through the more interesting parts of the earth’s crust that are known by geologists. Now look again at the diagram, and mark and fix in your memory some of the still more general divisions which geologists have made. From the lowest part of the figure to the bottom of the Silurian and Cambrian Systems (10th division) is represented the Primary Formation, the rocks of which are distinguished for the absence of the remains of living beings. From the top of the Primary to the bottom of the Coal is represented the Transition Formation, which is distinguished by containing the remains of plants and animals of low orders, almost all of which inhabited the ocean.
From the bottom of the Coal to the top of the Chalk is called the Secondary Formation, which contains the remains of abundant land plants, and of the first considerable air-breathing animals. These animals, however, were still of a low order, partaking much of the nature of lizards, turtles, and other reptiles, and were, for the most part, oviparous, that is to say, they hatched their young from eggs, and did not suckle them.
Then comes the Tertiary Formation, containing the remains of four-footed beasts, which produced and nourished their young as cattle now do, but most of which were still very different from any animals now on the earth. Then comes the Diluvial Formation, called also Drift, from the fact that it proceeded (as supposed) from a violent overflow of the ocean; and lastly comes the Alluvial, in which alone the bones of Man and of the existing races of animals are found. How wonderful is the order and method displayed in the works of the Creator!
I have thus given you a general description, which I can call only an approach to the real state of the case. Try to fix these general divisions, with their characters, in your minds, and in my next letter I will endeavor to describe things more as they actually exist.
“Letters About Geology,” by “Professor Pickaxe” (from The Student, June 1853; pp. 38-41)
My Young Friends:
In my letter in the last number of The Student, I gave you a brief description of the strata of earth and rocks which we should successively pass through, if we were to dig down through the outer portion of the earth’s crust, at a place where all the geological formations existed in their completeness. I hope you have carefully read that letter, and studied the diagram which accompanies it, as it gives you the foundation of the whole science of geology.
But having read it, and believing, of course, that no one has ever digged down so deeply into the earth as there supposed, you will ask, “How do you know that the successive layers of rocks are such as you have described them, and that they are of such enormous thicknesses?” I will try to answer this question to your satisfaction, in doing which I will introduce you to some still more interesting points in geological science.
First, then, I wish you to fix it clearly in your minds, that the stratified rocks (by which, as you will remember, we mean the rocks that are disposed in regular beds or layers, like the leaves of a book) consist simply of materials which were once carried in water, and which settled down to the bottom of seas, lakes, estuaries, or rivers, that once covered their places, and which, after thus settling down, became gradually hardened, as we now find them. All of these rocks, therefore, as you will perceive, must have originally been disposed on planes nearly horizontal. But they were afterward subjected to very great disturbances; and how those disturbances occurred you will be prepared to understand after we consider the original state of the unstratified rocks.
You must know, then, that the unstratified rocks, such as the Granite, the Trap, etc., were originally in a melted state from the action of intense heat. How this is proved I could not very well make you understand now, but proved it is, to the entire satisfaction, I believe, of all intelligent geologists. But as there was a time when there were no stratified rocks, and as the materials of the unstratified ones were originally in a melted state from heat, we are brought to the startling conclusion that all existing rock materials, and hence the whole substance of the globe, were once in a melted state—that the globe, in other
words, was originally one vast ball of liquid fire!
But you may conceive that during the lapse of time, this globe of melted matter would gradually cool and grow hard upon the surface, thus forming the first granite crust of the earth, while at some distance beneath the surface, the materials, not yet cooled, would still be in a melted state as before. The crust being once formed, a further cooling of the melted substance beneath would be attended, in some places, by a shrinking away from the crust, which would cause the latter, at those places, to fall in, while in other places, by chemical action, gases would be generated and the heat for a time so increase, that the crust would be liable to be violently thrown upward by an expansion from beneath. This falling in of the surface at some places, and forcing of it outward at others, would cause the appearance of mountains and valleys.
On the lower parts of the earth’s surface thus rendered uneven, the seas, lakes, etc., were formed, at the bottoms of which the materials of the stratified rocks were collected as the settlings from, and washings of, the water, as was before intimated.
Now these processes of caving in and heaving up of the earth’s crust often occurred in different places, also after the stratified rocks had been formed at the bottom of the waters, and the same movements on a small scale, occur even now, and are known as earthquakes. If you will, then, keep in view the fact that these in-fallings and up-heavings have occurred, more or less, in all geological periods, as well after the stratified rocks were formed as before, you will clearly perceive that from this cause those rocks may, in many cases, have been disturbed and thrown into almost every conceivable position, different from that in which they were originally formed; and you will thus begin to think it probable that large portions of the strata may, in some cases, have been broken and tilted up so as to expose their edges on the surface of the ground, thus enabling us to measure their thickness without digging into them. Now this is precisely what has taken place; and I will try to make the principles and processes more plain to you by the accompanying diagram.
The diagram represents a section, or up-and-down slice cut out of the earth’s crust. You will notice that, at each end, there is a high place, or mountain, and that in the hollow between the two the strata appear. All the white or unshaded part of the diagram, under the strata and at either end, represents the Granite, which, as before intimated, is the oldest of all rocks. But before the strata commenced to be formed, all this rocky foundation was nearly level and horizontal, with only a sufficient hollow in the center to form the bed of a sea. At the bottom of this sea, the first series of strata, and the lowest which you see in the figure, was formed.
When this formation was complete, the granite at the left end of the diagram was crowded upward by a force from beneath, and as it went upward it bent the series of strata which lay upon it into its own shape, and carried one end of it nearly as high as it went itself. The rock, or mountain, however, was not at first elevated so high as it is now; but after its position was thus altered with reference to the sea basin, the second series of strata began to be deposited in the water, in the same manner with the first, but having their ends partly resting against the surface of the first strata now bent upward, as you will find represented if you look on the left side of the basin.
After the second series of strata had been completed, the granite mountain on the left side was thrown up still higher, bending the first strata to a nearly perpendicular position, and in the movement it bent upward the left end also of the second series from the previous horizontal position, as you will likewise see represented in the engraving. Then the third, and fourth, and so on to the last, series of strata were in like manner deposited in the same basin.
But let us now attend to some other points. Under the left end of the basin you will observe a vein, which appears as if it had been shot up from beneath through the hardened granite, cutting directly through the first series of strata, and extending above the bottom of the second. This represents a vein (or “dyke,” so called) of Porphyry, a primary rock not so old as the Granite, which, in a melted state, forced its way upward through the overlying rocks, and flowed over the surface before the second series of strata commenced being formed. The vein which is seen to arise from beneath, near the middle of the basin, is a vein of Trap rock, a newer rock than the Porphyry, and which in like manner, in a melted state, forced its way up through the overlying rocks, and flowed over the surface before the rocks above it began to be formed.
After this the Lava, which is the newest of the primary rocks and the product of existing volcanoes, for a long time strove to escape from its under-ground prison where its quarters became too narrow, and, in the madness of its desperation, it made a tremendous effort, shaking the whole globe, and pushed up the granite which lay upon its top into mountain heights, forcing a passage through the cracks and fissures and flowed over the top, forming a volcanic crater through which it has till this day been spouting and bellowing as if in very triumph over the forces which strove to confine it to the deep! In its strivings for vent it not only threw up the Granite, but the overlying stratified rocks, bringing their broken edges to the surface, as you may see them represented at the right side of the basin.
I have now the means of convincing you that the thickness of the stratified rocks, as well as the general order in which they occur from lowest to highest, or from oldest to most recent, may be approximately ascertained without digging into the earth in the manner which, for illustration, was imagined in our previous letter. The distance across the upturned edges of the strata which are to be seen on different portions of the surface of the earth (as represented on upper surface of the diagram, right side of the basin) can, of course, be measured, and then by finding the angle at which they are inclined, or, in other words, by observing how much they lean, their thickness perpendicularly through may be easily calculated.
But seldom, if ever, are the broken edges of all the strata of the earth found exposed at the surface, in one unbroken series; but parts are found here and parts there in such relations, and with unmistakable marks of proof that they belong to each other. The general order in which the different rocks occur, as lower and higher, is the same all aver the globe; and it is by adding the thickness of those we find here, to the thickness of those we find there, that the aggregate thickness of the whole series is made out.
If you have apprehended what I have written above, and what I stated in the previous letter, you doubtless already begin to think, with me, that Geology is a most sublime and beautiful science; and if you follow the advice of your sincere old friend, Professor Pickaxe, you will not dismiss this subject from your mind until you have mastered it pretty thoroughly, and thus
acquired the means of appreciating a thousand interesting objects with which you will meet in your rides or walks through the country. A knowledge of its principles will enable you to read an epic in a mountain, a history in a sand-bank, and a sermon in a stone. Ponder these matters until my channel of communication with you opens again, and then I will tell you something more which ought to interest you.
“Letters About Geology,” by “Professor Pickaxe” (from The Student, July 1853; pp. 73-76)
My Young Friends:
The descriptions of the earth’s outer coating, given in my First and Second Letters, were little more than descriptions of rocks, their modes of formation, the disturbances to which they have been subjected, etc. I have shown you that a great portion of the earth, to those depths from which flow the melted materials of the unstratified rocks (such as the lavas, and formerly the trap, etc.), is composed of this hardened form of material. After these descriptions, you will naturally expect me to say something about the soil, with its origin, mode of formation, etc., and accordingly this shall form the leading subject of the present letter.
The term, soil, is commonly used to signify that thin stratum of dark earth, mixed with decayed vegetable and animal matter, which constitutes the immediate surface of the ground; but in the present communication we propose to consider the term in its most comprehensive sense, as signifying all earthy matter that is not consolidated into rock.
The soil, in this sense of the term, varies from a few inches or feet to several hundred feet in thickness; though of the latter thickness it is seldom found, except in fissures and gorges between the broken rocks, where it has been deposited by the agency of floods.
The soil now existing is mostly of the alluvial and diluvial formations, and, with the exception of the decayed vegetable and animal matter that is among it, it is composed of the materials of previously existing rocks, which were reduced to fine fragments and to powder by agencies to be hereafter described.
It must necessarily be supposed, that soil existed in each geological period in which vegetable and animal life prevailed; for without it no living being could have found sustenance. The soil of one period, however, became, by process of consolidation, the rock of subsequent periods, to be re-decomposed, perhaps, to form other soils; and of the agencies and processes
by which solid rooks have been reduced to soils, in all ages, I will now speak.
This subject will be understood by first considering that the surface of the earth, in all geological ages after the cooling and hardening of the original granite, has been in frequent contact with water, by which large portions of it, indeed, were, for long periods, entirely covered, while other portions were constantly subjected to the action of the atmosphere.
The earth, moreover, has, probably, in all ages, been traversed by electrical currents, and since the period of the New Red Sandstone formation, more especially its surface, in its higher latitudes, has been subject to alternating heat and frost, owing to the increasing and diminishing action of the sun’s rays upon it. The action of all these agencies could not do otherwise than exert a decomposing influence upon the most solid rocks; but let us consider the operations of these forces, singly and collectively, a little more in detail.
In my Second Letter, it was shown that the materials of all primary unstratified rocks were originally in a melted state, from the action of intense heat. It was also shown that, after these cooled down and hardened upon the surface, and were sometimes covered deeply under the subsequently formed stratified rocks, the melted materials of the granite, porphyry, trap, and other unstratified rocks, still lying deep under the earth’s surface, would generate gases, and expand by an increase of heat, and thus frequently burst upward with great convulsions through the hardened masses which lay upon them, discharging their red-hot substances upon the surface.
These eruptions frequently occurred at the bottom of oceans, causing them, for many miles in circumference, and for long periods, to boil like a cauldron. This explosive, spouting, steaming, foaming, and bellowing operation must have been attended by the reduction of large quantities of rock into fragments, pebbles, sand, and mud, which, being carried by the violently excited currents, and deposited in places of more quietude, formed the basis of those submarine, or under-sea soils, which constituted the fitting conditions for the origin of sea-plants and animals.
These remarks, applicable in some degree to all geological periods (for even now we frequently have volcanic eruptions in the ocean), are intended especially to apply to the more ancient periods, when the ocean covered almost the whole surface of the globe, as it is evident that it did from the fact, that scarcely any place, save the naked granite mountain, is destitute of some trace of its former presence. Afterward, however, large portions of the earth’s surface, previously overflowed by the ocean, were thrown up into continents and islands, and throughout long subsequent geological periods were exposed to the atmosphere, the rains, the frosts, etc.
But, previous to speaking of the results of these agencies, operative in our own as well as in previous periods, I will speak briefly of a remarkable display of forces, principally mechanical, which appears to have occurred just previous to the introduction of man upon the earth, and which resulted in the production of those vast quantities of soil, or loose earthy matter, which constitute the Diluvial Formation.
From causes which, perhaps, no human being will ever be able to fully determine, a remarkable coldness in the earth’s atmosphere appears to have suddenly occurred, about the close of the Tertiary Period. It may seem strange to you that man should presume to determine what was the state of the climates upon the earth so long before the human race could have had an existence, but, strange as it may seem, this fact may be stated with an assurance approaching to absolute certainty.
Among other circumstances which might be cited as proof, we may here incidentally mention that, in the year 1771, the entire carcass of a rhinoceros was found in the frozen diluvial deposits of Siberia; and, about the beginning of the present century, the carcass of a large species of elephant, called the mammoth, was also found incased in the perpetual frosts of that country, and in such a perfect state of preservation, that the natives fed their dogs upon its flesh!
These were animals of species different
from the rhinoceros and elephant of this day, and their kind is not known to have existed on the earth since man was created. They were animals, moreover, which could have lived only in a warm climate, and numerous bones of their species found in Siberia, together with other circumstances, show that they were inhabitants of that country, and were not transported from more southern regions. The climate of that extreme northern country, then, at the period referred to, must have been comparatively warm, and the change of temperature must have been so sudden, as to destroy those animals and entomb them in frozen matter, before their bodies had time to decompose.
This change, from a warm to an intensely cold temperature, seems to have occurred all over the polar and temperate regions of the earth, while there appears to have been, at the same time, a sudden sinking down of the land in all those regions, so as to become overflowed by the ocean. Moreover, while the ocean thus overflowed the existing lands, it seems to have abounded with enormous icebergs, such as those which are even now frequently seen floating in the northern parts of the Atlantic Ocean at certain seasons of the year.
These icebergs, sinking deeply beneath the surface of the ocean, would frequently strike upon the ground, and scraping over its surface, tear large masses of rock from their original beds, while the clashing and friction accompanying the process would round off their sharp corners, and reduce large quantities of them to pebbles, sand, and mud. Sometimes these fine materials, with large masses of rock, would be thrown upon the tops of blocks or projections of lee, and floated to great distances and scattered over the country.
Frequently large pieces of rock, torn by these forces from the beds to which they originally belonged, have been carried over steep and high mountains, and sometimes lodged upon their summits or scattered over their southern declivities, where they are now found; and the long-continued passage of the ice bearing these rocky fragments, has worn scratches and sometimes deep grooves in the stable mountain rock.
These scratches and grooves may be distinctly seen at this day on the summit of almost every mountain where the rock is not covered with soil. They all run in one general direction, which is nearly north and south, which proves that such was the general direction of the currents which transported those masses.
These huge masses of floating ice, mixed with stones and large pieces of rock, must have had the effect of an enormous rasp rubbing over the rough surface and high prominences of the earth, and filing them down to comparative smoothness; while the sand, gravel, mud, and clay resulting from the process, were carried by the currents and deposited over the surface of the sea-bottom, filling up deep hollows and reducing the face of the ground from a previously rugged and uneven, to the comparatively level state which it now presents.
After this process was completed, another convulsion of nature seems to have taken place by which the land was again raised to the surface and the sea made to retire, leaving the earth covered with what we call the Diluvial Formation, or a formation resulting from a deluge.
It may be very hard, my young friends, for you at first to conceive of these mighty operations; yet rest assured that all the most learned geologists of the age would not tell you they had actually taken place were there not the most satisfactory proofs of the fact. As your minds expand by the study of this sublime subject, you yourselves will see and appreciate these proofs in almost every bank by the roadside, and in almost every excavation for a cellar or a railway; for the diluvial deposits, be it remembered, are strewn over almost all the northern and temperate regions of the globe, and it is said also over corresponding latitudes in the southern hemisphere. It was by this benevolent provision of the Divine Creator that the greater portion of our existing soil was formed, and that the earth was rendered a suitable habitation for its tenant, man, who was created soon afterward.
But the decomposition of rocks into soil is still slowly going on according to processes, some of which have been in opera-
tion in almost all geological periods. You may understand what agency frost, in connection with water, has in this process, by soaking a soft brick in water, and exposing it on a cold winter’s night until it freezes, and afterward letting it thaw. You will find that on thawing it will all crumble into powder. This is an operation which all soft and porous rocks near the surface of the ground constantly undergo during winter, though the action is slight and confined to their surfaces moistened by the water.
You may understand, too, what agency the rains have in the reduction of rocks to soil, by observing that the hardest stones which have long lain under the eaves of a house, have grooves worn in them by the water dropping on them from the roof in rainy weather. This is the origin of the saying, “Constant dropping wears away stones.”
You will also understand the agency of the air, in connection with alternating moisture and dryness, in decomposing rocks, by observing that the face of the hardest rocks, after having been long exposed, wear a dingy appearance, different from the color of the rock inside, as you will find by breaking off a fragment. This dinginess at the surface of the rock is caused by the fact that a slight coating of it is already turning into earth, which you may ascertain by scraping it with a knife. These dissolved particles of the surface are being constantly washed off by the rains, and incorporated with other portions of the soil.
Of course, one very important source of the soils now being formed, is the vegetable matter which is constantly accumulating and decaying on the earth’s surface. But this point my intelligent young readers doubtless already understand sufficiently; and I may here only add, that without some admixture of vegetable or animal matter in a soil, no kind of plants will grow well from it.
These are the principal modes of the origin and production of the soil. If you have duly understood and appreciated the foregoing remarks and explanations, I think you can not feel otherwise than deeply interested in the general theme and its various sublime relations; and hoping that you will think over these points until you have fixed them in your memory, I must bid you good-bye until my next.
“Letters About Geology,” by “Professor Pickaxe” (from The Student, August 1853; pp. 104-106)
FOSSIL VEGETATION—COAL FORMATION.
My Young Friends:
My last letter was devoted to the consideration of the origin of soils: following the natural order of progressive thought, I shall now offer some general remarks respecting that immediate outgrowth from the soil called vegetation, and especially respecting that remarkable development of the vegetable kingdom the remains of which, covered with rocks afterward formed, have been preserved until this day, and constitute what is called the Coal Formation. That this subject may be properly appreciated in its general bearings, the origin, general economy, and uses of vegetation, should first be made the theme of a few remarks, in doing which some important dependencies of animal life will also be incidentally brought into view.
Between the vegetable and animal kingdoms there is an admirable interchange of offices, and a mutual subserviency to each others wants. That this may be fully understood, we must take into consideration the constitution and properties of the elements on which both kingdoms depend for their subsistence and growth.
There is in the air which we breathe, as many of you have already learned, an element called oxygen. This is mixed with another element called nitrogen, in the proportion of about 21 parts of the former, to 79 parts of the latter. Now, oxygen is the supporter of all animal life, and also of all ordinary combustion: without it no animal nor human being could live, nor could any fire burn. But by being breathed by animals, and absorbed by burning substances, oxygen unites with carbon (which is the substance of coal), and forms a compound gas called carbonic acid. This gas, therefore, is constantly, with other gases, being breathed forth from the lungs of all men and animals, and is constantly rising from all fires, and mingling with the air of which it, therefore constitutes a third ingredient, though its proportion to the other ingredients is small.
Now, understand that while oxygen is necessary to all animal life, and all flame, carbonic acid, in its pure, or nearly pure state, instantly destroys the lives of animals which breathe it, and as instantly puts out fires with which it comes in contact. But mark well that this substance, so fatal to animal life and to combustion, is quite as necessary to vegetable life as oxygen is to animal life. It is absorbed by the leaves of plants and trees, and the carbon that is in it becomes solid, in the form of vegetable fiber, thus promoting the growth of the plant or tree, while the oxygen, which went to compose it, is given back to the air.
Thus while the breathings of animals and the exhalations from fires continually tend to poison the air by infusing into it carbonic acid gas, the breathing of plants, as it may be called, as constantly tends, on the other hand, to purify the air by decomposing the carbonic acid, and giving forth new supplies of oxygen; and the carbon taken from this gas, and solidified in plants and trees, at the same time furnishes new supplies of fuel and vegetable food. Thus by this most admirable contrivance of the Creator, the animal and vegetable kingdoms are made to mutually contribute to the support of each other; and thus the natural conditions on which both depend for subsistence are made to maintain their own balance!
Now be it understood that before the vegetable kingdom commenced to be developed, the immense quantities of carbon which subsequently became solidified in it, must have existed, in connection with oxygen, in the air, in the form of carbonic acid gas. In this state of things no air-breathing animal could have existed upon the earth’s surface for a moment—while the great abundance of carbonic acid, at the same time, afforded one condition extremely favorable to vegetable growth.
At first, however, the sea appears to
have cvered neavly the whole surface of the earth, and the atmosphere, loaded with thick carbonic and watery vapors, was as a mantle of darkness, in a great measure excluding the rays of the sun. While oceans and darkness thus enveloped the earth, the carbon, with which the atmosphere was excessively loaded, could, of course, but slowly assume forms in the vegetable kingdom, nor could the forms at first assumed be of a very high grade.
Accordingly the first vegetation, the remains of which became entombed in the rocks, to be preserved until the present day consisted of sea-weeds, the most prominent of which were of species called fucoides. It is probable that still simpler species of plants than these existed in periods earlier, but on account of their frail and perishable nature, no impressions of them have been preserved in the rocks.
During the general submergence of the earth’s surface under the waters, which condition obtained more or less throughout the long periods that were occupied in the deposition of the Cambrian, Silurian, Old Red Sandstone, and Mountain Limestone systems,* the vegetation was, of course, almost exclusively such as could grow only under water, and was hence of a low order. But after the deposition of the rock-systems just named, and at the beginning of the Coal Period, extensive tracts of land appear to have been slightly elevated above the level of the sea—so slightly as to be subject to frequent and long-continued overflowings of the waves.
* See Diagram accompanying Letter L.
By this time immense quantities of carbon, which, combined with oxygen, had previously existed in the air, had descended and become solidified, not only in the vegetable formations of the ocean, but in the vast quantities of lime, forming thus the extensive masses of corbonate of lime, or lime-rock, that are interstratified among the older formations. With the descent of so much carbon and carbonic acid, with watery and other vapors, which must have the greatly abounded in those early periods, the atmosphere had probably at that time become sufficiently clear to admit of the descent of a considerable degree of sunlight to the earth; and under its genial influence the rankest and most rapid vegetation seems to have grown up upon the low marshy plains which often extended far back from the borders of the sea.
The rapidity of the growth of this vegetation was promoted by constantly prevailing moisture, by a warm and unvarying climate, and especially by the immense quantities of carbonic acid gas with which the atmosphere was still loaded, and on which, as we have before seen, vegetation subsists, as animal life subsists on oxygen. Crop after crop of soft and juicy plants thus rapidly grew up, came to maturity, and sank to the ground; and stratum after stratum of vegetable matter was thus formed.
After thick accumulations had thus occurred, the whole must have been submerged under the ocean, and covered over by a stratum of mud and sand washed up by the waves, the whole vegetable wealth being thus securely stored away for the future use of man!
Then, again, the waves having receded, the dry land would reappear, and the process of vegetable accumulation would be repeated, the product being afterward sunk under the waters, to be covered up by a stratum of mud and sand as before; and so by alternate elevations and submergences of the land, and accumulations and confinements of vegetable productions, the aggregation of the materials of the whole Coal Formation was finally completed.
Many of you will doubtless be surprised to be informed of the extent of these deposits of vegetable matter that were afterward turned into coal. They are found, more or less, in almost every country of any extent upon the face of the earth, but it will suffice to give a description of their extent in the United States, where, perhaps, they are more largely developed than in any other country. I give this description in the language of Professor Hitchcock, who says:
“The anthracite deposit of Pottsville (Pennsylvania) is 60 miles long and about 5 broad: that of Shamokin, commencing near Lehigh, is of the same length and width; and that of Wilksbarre is 40 miles
long and 2 miles broad. In some instances a single seam of coal in these strata is 60 feet thick; and near the middle of the valley, between the Sharp and Broad mountains, no less than 65 seams have been counted.
“The bituminous coal field, embracing the western part of Pennsylvania, and a part of Ohio, extends over an area of 24,000 square miles: the largest accumulation of carbonaceous matter probably in the world. In fact the bituminous coal measures can probably be traced, almost continuously, from Pennsylvania to the Mississippi, and even into Missouri, 200 miles west of that river.
“Indeed, coal exists on the eastern slope of the Rocky Mountains; and it would not be strange if this should be found to be the western outcrop of coal-bearing strata, whose eastern extremity is in Pennsylvania. …. The world can not furnish a parallel to this immense mass of carbonaceous matter, to say nothing of the smaller deposits in Henrico, Chesterfield, and Prince Edward counties, Virginia; those in Nova Scotia and New Brunswick, and that of anthracite in Rhode Island and Massachusetts.”*
* Hitchcock’s Geology; p. 330.
There are a few deposits of coal among rocks formed both before and after what is called the Great Coal Formation, but these are not very extensive or important, and we omit a further mention of them.
Here, my young friends, is a display of Goodness and Wisdom of the Divine Creator, which, I hope, will not fail to excite your attention—Goodness in thus laying up inexhaustible stores of fuel for the race of mankind intended afterward to be created, and Wisdom in so directing this process as to effect by it those changes in the previously thick and unwholesome atmosphere, which fitted it for the introduction of higher types of organic life, both in the vegetable and animal kingdoms, and finally for the introduction of man, the last and highest of created beings.
You may conceive of the changes that were produced in the constitution of the atmosphere by the incalculable growths of vegetation that were successively produced, and entombed in the earth, during the Great Coal Formation, by first conceiving what would be the result if all the coal now existing were burned in a day. The atmosphere would in that case be so loaded with carbonic acid gas, that no animal with lungs could live for a moment!
That same carbonic acid gas which would result from such a combustion, must have existed in the air before the coal was formed; and this of itself is a sufficient reason why the only animal remains now found in the rocks of that period are of such creatures as lived either wholly or in part in the water, such as fishes, frogs, etc., and which the external air does not affect.
With the completion of the Coal Formation, the atmospheric conditions were so far changed as to admit of diversities of climates, and the alternations of winter and summer, rain and sunshine, etc., all of which, strange to say, have left their unmistakable imprints upon the rocks. If circumstances permit, I shall be very happy, in a future letter upon the animals of the geological periods, to describe to you the indications by which it is now known that such diversities and changes did then occur.
The plants of the earlier fossiliferous periods were, as already remarked, mostly such as grew in the sea. The plants of the coal period were mostly flowerless and of low orders, among which mosses, ferns, equiseta (or horse-tails, as their living representatives are called), and several members of the coniferous or pine family, were conspicuous. In the successive formations above, the higher forms of vegetation more and more prevail, until, in the higher parts of the Tertiary Formation, we find the remains of Poplars, Willows, Elms, Chestnuts, Sycamores, Oaks, etc.—showing a gradual “shading off” into the kinds of vegetation now growing on the earth’s surface.
With this very brief description of the more prominent forms of vegetation that were successively brought into being during the “six days,” which geologists generally understand to mean “six grand periods” of creation, I take my leave for the present.
“Letters About Geology,” by “Professor Pickaxe” (from The Student, October 1853; pp. 165-167)
My Young Friends:
Having in my last letter called your attention to the progressive creation of the Vegetable Kingdom, as indicated by its remains found in the rocks, the next subject naturally in order will embrace similar considerations relative to the Animal Kingdom. This department of the Creator’s workmanship, embracing all animated forms, whether existing upon land or in water, has, hy naturalists, been divided into four general classes, respectively termed the Radiata, the Mollusca, the Articulata, and the Vertebrata.
The Radiata embrace those lowest and most simple forms of animal life which are characterized by projections or radiations from a common center, somewhat like the roots and branches of vegetables. Of this class the star-fish, found along our sea coasts, and also the sponge, may serve as living examples—for the sponge is the skeleton of an animal of this low order, though many of you may not have hitherto been aware of the fact.
The Mollusca, or soft animals, as the name implies, comprise shell-fish and all those animals of a soft texture which have no jointed shell or back bone. The clam, the oyster, and the cuttle-fish, or “squid,” as it is sometimes called, are among the living examples.
The Articulata comprise all those animals that have regularly jointed or articulated shells, or other external coverings. Lobsters, crabs, shrimps—also bugs, flies, bees, and other insects, belong to this class.
The Vertebrata comprise all those animals that have regularly jointed back bones, of which you will find familiar examples everywhere, both on the land and in the water.
These general divisions not only apply to existing races of animals, but to those very different forms and species of the animated kingdom whose various races were successively created and destroyed long before man came into being. That the very brief and general description which I am about to give of these latter may be the more clearly apprehended, and the more permanently remembered, it would, perhaps, be well for you to open before you the diagram that accompanied my first letter,* and follow me upward through the strata as I designate the localities in which the fossils to be described are mostly found.
* See the May number of The Student.
In the oldest or primary rocks, as I have before said, no traces either of animals or plants have yet been discovered. They first begin to appear in the lower or oldest part of that group of rocks known as the Cambrian system. From the discoveries which have yet been made, it is difficult to say what particular class of animals was first brought into existence. The older fossils, however, belong exclusively to such animals as dwelt in the sea, and these were, for the most part, of a low and simple character.
It would seem probable, according to the general law and order of progress, that the Radiata preceded the rest upon the stage of existence, and that the first species of these were of the smallest and most imperfect kind, and so loose in their texture as to be subject to entire decay, leaving no traces of their forms which could afterward tell the tale of their existence. In point of fact, however, the remains of Radiata, of Mollusca, and of Articulata appear in very close connection in the oldest fossiliferous rocks that have yet been discovered, though the next higher class—the vertebrated fishes—probably did not come in until some time afterward.
The Radiata, whose remains are found
in the older fossil bearing-rocks, consisted for the most part of coral insects and crinoids. Coral insects (which come under the generic name of polypi) are those curious little creatures which elaborate that limy substance called coral, and with which most of you are familiar. Continuing this work with untiring industry from age to age, they build up stony structures from the bottom of the ocean, which sometimes extend over areas of thousands of square miles. These abound extensively in the tropical regions of the existing seas, and especially in the South Pacific Ocean where they have formed the bases of many islands. Species of them seem to have existed in all the fossiliferous ages, and their work forms an interesting chapter in the geological history of our globe.
Crinoids grew upon a jointed stem from the bottom of the ocean, and were of a very curious structure. The most remarkable one, whose remains are found in the older fossiliferous rocks, is called the Lily Encrinite, from the resemblance of its fossil to a lily.
The stem of the lily encrinite, consisted of a vast number of little bones so jointed together as to render it very flexible, enabling it to reach about in all directions for those floating substances which constituted its food. Upon the top of this stem or column was supported the main body, which was of a cup-like form, and from whose margin proceeded five arms, having numerous joints, and dividing into fingers surrounding the mouth. With these arms and fingers it seized its prey and passed it into its cup-like body, where it was digested, its nourishment extracted, and the refuse substance thrown out through the same channel by which the food first entered. The number of little bones or joints composing the body of one of this species has been estimated at twenty-six thousand. The skeletons of these curious animals enter so largely into the composition of the older limestones, that they have, from that fact, been called Encrinal Marbles.
The Mollusca, or shell-fishes, abounded so extensively in the earlier fossiliferous periods, that deposits of limestone, sometimes many hundred feet thick, and covering areas of hundreds of square miles, seem to be made up almost entirely of their shells. In fact, whole mountains, sometimes thousands of feet high, seem to be composed principally of these shells, the same having been heaved up from the bottom of the ocean to their present position, by volcanic agency.
Though these shell-fishes were all different from any species now living, and some of them were very curious, they bore a sufficient resemblance to those of existing tribes to render particular descriptions unnecessary for the purposes of the present sketch.
Of the Articulata which inhabited the more ancient seas, the Trilobites are by far the most remarkable. They are called Trilobites from the fact that their bodies consisted of three lobes, which are divided from each other by furrows running from head to tail. In other respects their shell or covering is analogous to that of the Lobster. The remains of several species of these animals have been found, the smallest of which is about an inch, and the largest about twenty-one inches in length. They are found in the older fossiliferous rocks (the Cambrian and Silurian series) in all the northern parts of Europe, in North and South America, at the Cape of Good Hope, and elsewhere. They were thus among the earliest living inhabitants of our globe; but I believe that not a trace of them has been found in the strata above the Coal Formation.
The Trilobite is remarkable for being one of the first, if not the first, animal that possessed eyes; and these eyes were again remarkable for consisting of numerous small lenses similar to those constituting the eyes of insects and other articulated animals now living. The existence of eyes in these creatures is a valuable fact, leading to the inference that light prevailed, at least to some extent, in that early period in our earth’s history—though it is probable the sun’s rays had not yet shone directly upon the earth, through the atmosphere rendered thick and turbid by the carbonic and other vapors with which it was overcharged.
Fishes, properly so called, I believe have not been found in the older fossiliferous deposits, though on this point there has
been some dispute. They occur, however, in abundance in some members of the Silurian rocks, and in the Old Red Sandstone Formation. Moreover, among the first fishes which appeared, there were probably few, if any, that were properly vertebrated. Instead of possessing a regularly jointed back-bone, they had, in its place, a mere gelatinous cord running from head to tail, similar to the spinal cord of the shark or the sturgeon which inhabit our modern waters. Vertebrated fishes, however, are of frequent occurrence in the upper members of the Transition rocks, and with their creation was completed the marine division of the four grand classes of animals mentioned at the beginning of this article.
But during all these immense periods there were no land animals, or animals which breathed the air. This was simply because the air, as shown in a former letter, was not fit to be breathed before the great Coal Formation, owing to the great excess of just such vapors as now result from the burning of coal, and which you know can not be breathed long without destroying life. The land animals, which were afterward gradually introduced, as conditions became suited for them, were of a still more interesting character; but as I have already occupied space enough for one letter, I must reserve the general description of these for another.
“Letters About Geology,” by “Professor Pickaxe” (from The Student, November 1853; pp. 4-6)
FOSSIL ANIMALS, CONTINUED.
My Young Friends:
In my last letter I gave a brief description of some of the most remarkable animals which existed before the Coal Period, and whose remains are found in the transition series of strata under the coal, as represented in the diagram accompanying my first letter.* You will bear in mind that these animals were all dwellers in the ocean. Land animals, or animals that breathe the air, did not make their appearance in any considerable numbers before the Coal Formation, because of two unfavorable circumstances already mentioned: first, the earth before that period was almost entirely covered with water; and secondly, the air was too impure to be breathed.
* See May number of The Student.
There have been found, however, a few traces of a small lizard-like reptile, of a kind which sometimes lives in the air, and sometimes in the water, found among the upper members of the Old Red Sandstone Rocks in Scotland, which rocks, as you will remember, are under and considerably older than the Coal. Tracks of wading birds and of frog-like creatures have also been found impressed upon strata belonging to the Coal Formation in Pennsylvania; but all these may be considered as exceptional developments, owing to the favorable circumstance which happened to exist in particular places of small extent; while land animals, as a grand class, did not take a decided and permanent stand among organized beings until the periods after the Coal, and when the air had been rendered breathable and comparatively pure by the formation of that substance.
On the layers of the New Red Sandstone (which you will recollect constitute the next formation above the coal) there are found in various places numerous tracks of birds, tortoises, and frogs. The Sandstone in the valley of the Connecticut River presents remarkable examples of these tracks; and they are also found upon the corresponding rocks in particular parts of Scotland, England, and Germany.
The rocks bearing these footprints are sometimes quarried out fifty or a hundred feet or more below the surface of the earth. Some of these tracks are very small, the toes not being more than half an inch long, and the length of the step being not more than three or four inches; while others are of an enormous size, the foot being seventeen inches long, and the length of the step being from four to six feet. In the largest species, indeed, the whole length of the track is two feet, and of the step six feet.
What wonderful creatures must these have been! The largest of them must have stood from twelve to fifteen feet high, and could probably have carried half a dozen of my young readers on their backs as easily as a horse can carry his rider. These huge creatures, solemnly pacing back and forth upon the borders of the ancient seas, accompanied by great frogs of the size of an ox, and tortoises of equal bulk, together with inferior gradations of birds and reptiles, all the way down to the size of the tiny sand-piper or the toad, would have presented a curious spectacle to a human being, had such then existed upon the earth to witness it!
Those of you who may hereafter visit the geological cabinet of Yale College, New Haven, may find some interesting specimens of rocks from the Connecticut Valley, bearing these footprints; but if any should find it convenient to visit the sandstone quarries almost anywhere along the Connecticut
River above Middletown, they may possibly have, the good fortune to see some of these impressions hi the rocks in their proper places.
As we ascend in the strata, the remains of still more curious animals meet our view. Before the completion of the Old Red Sandstone, indeed, there were, as we have before seen, some small and inferior species of Saurians, or lizard-like animals, in existence. These, again, appear in superior forms in the New Red Sandstone, having probably been continued in some of their species through the intermediate periods of formation. This general class of creatures, however, did not attain to its full development until the Lias and Oolite periods, which came in immediately after the New Red Sandstone. More than fifty species of Saurian remains have been found in those rocks; but of those which have excited the greatest wonder and astonishment, I have room here to briefly describe only three, viz., the Ichthyosaurus, the Pterodactyle, and the Iguanodon.
The Ichthyosaurus (which name signifies fish-lizard, and of which there were several species) was sometimes more than thirty feet long. It had a backbone like that of a fish, a head and tail similar to those of a lizard, with a long tapering snout, and jaws sometimes containing as many as one hundred and eighty sharp teeth. Its eyes were enormously large, in some species measuring fourteen inches the longest way. It had four oars or paddles projecting from its sides, like those of a whale, with which it was enabled to urge itself rapidly through the water, which was its element. Its food was fish and the young of its own species.
Figure 1 represents the animal as it must have appeared while living; but those of you who can make it convenient to visit the Crystal Palace Exhibition now open in New York city, may find, in the Mineralogical department, two or three interesting though small specimens of the fossils of these animals, as they are now found petrified in the rocks.
The Pterodactyle was a small animal of a still more curious structure. It may perhaps not improperly be called a winged or flying saurian, though some would doubtless hesitate to place it in the Saurian family. It had the head and neck of a bird, the mouth and teeth of a reptile, and the wings of a bat, from the fore corners of which projected claws or fingers, which probably enabled it to cling to rocks and other supports, and also to climb. It probably fed chiefly on insects which it caught while flying through the air, and it is thought that it also had the power of diving for fish.
Of all the animals of the ancient world this probably is the least resembled by any species now living. In familiar phrase, it can scarcely be considered as either “fish, flesh, or fowl,” and by some it has been pronounced a monster; but Cuvier, the French naturalist, has shown it to be a beautiful example of that divine wisdom which adapts creatures to peculiar conditions in the outer world. Figure 2 represents the animal as it must have appeared while living.
But the most enormous of all the animals of the ancient world, and probably the largest of land animals that ever existed upon the globe, was the Iguanodon. It was a
large saurian or lizard-like animal, whose average length could not have been less than seventy feet, and Dr. Mantell, its first discoverer, thinks that some individuals must have exceeded one hundred feet. The circumference of its body was fourteen and a half feet; the length of its tail was more than fifty feet, and the circumference of its thigh more than seven feet! The structure of its body shows that it lived upon the land, and the form of its teeth proves it to have lived on herbs. Its general form almost precisely resembled the Iguana, an animal now living in the West Indies, with the exception that the length of the latter is only about five feet. Figure 3 represents the Iguana, which, if you imagine it magnified to the length of from seventy to one hundred feet, will give you some idea of the huge creature which trailed its length along through the forests and jungles of the ancient world.
Other interesting creatures of the Saurian family might be mentioned as among the conspicuous animal forms of that period, but those which have been described will serve as general types of the rest, and will give you some idea of the character of organic life in those early times.
I wish to impress it distinctly upon your minds, that all these animals were of classes which hatch their young from eggs, and that it was not until pretty late in the general period under consideration that any animals existed the young ones of which were born alive. But remains of probably the first and oldest animals of the latter class have been found in England, in rocks called the Wealdin rocks, and which were deposited in fresh water, probably during the period when the Oolite rocks were being formed.
The animals referred to are called Marsupials, which means animals with a pouch; because, like the living opossum and kangaroo, they had a pouch under their bodies in which their young were nestled and nourished for some time after they were born[.] Though viewed in one light, therefore, it may be said that their young were born alive, yet viewed in another light, it can scarcely be said they were then more than half born; and they show a wonderful link of transition between the egg-hatching and the higher class of animals, which latter did not fairly come in until the commencement of the next general period, which was the Tertiary Period, the formations of which are represented in the diagram accompanying my first letter.
Of some of the most wonderful animals of the Tertiary Period a brief description will be given in my next letter.
“Letters About Geology,” by “Professor Pickaxe” (from The Student, December 1853; pp. 40-43)
My dear young friends:—
In my last I described some curious specimens of the animal remains found principally in the Secondary series of rocks. I will now finish this series of letters with a rapid survey of the principal animals which dwelt upon the earth during the formation of the Tertiary strata.
In the lowest of these strata we find the remains of the first known animals (except the pouched or opossum-like creatures before described) the young of which were born alive, and nourished from their mothers’ breasts. Among these were several clumsy-looking creatures with thick skins, the remains of which Cuvier found in the strata on which the city of Paris is built. Perhaps the most remarkable of these was the Palæotherium Magnum, so called, which means the great ancient beast. It was about the size of a horse, but its body was more thick and clumsy, and its legs were shorter in proportion. It probably had a trunk like an elephant.
There was also associated with the above a lesser beast, of similar general form and character, called the Palæotherium Minus, and which was about the size of the deer; and besides these there were about forty other species more or less resembling these, found in the same strata, which are the oldest of the Tertiary. Their organizations were low and gross in comparison with many of the quadrupeds that were afterward created.
These, be it observed, were animals totally unlike any now existing upon the earth; but in the same general division of the Tertiary, a little higher up, there have been found animals resembling the hog, others resembling the hedgehog; also the bat, wolf, fox, racoon, squirrel, dormouse, and serpents,—and of the bird tribes, the buzzard, owl, quail, woodcock, sea-lark, curlew, pelican, albatross, and vulture, together with many genera and species, both of quadrupeds and birds, which ceased to exist long before man made his appearance.
In the next ascending division of the Tertiary has been found probably the largest of all four-footed animals that ever inhabited the earth, the Iguanodon described in my last letter being alone excepted. It is called the Dinotherium, which means terrible beast, and presented a form similar to that seen in the above engraving.
This animal is considered as having sustained a position between the tapir and the mastodon. Its length was about eighteen feet. It had two enormous tusks proceeding, and curving downward, from the end of its lower jaw, by which it was enabled to dig up the ground in quest of
roots, which the structure of its teeth proves to have constituted an article of its food. Its general form, however, shows that it lived principally in the water, like the hippopotamus, and it probably used its tusks to rake up the plants and roots from the bottom of the lakes and rivers in which it dwelt. By means of the long trunk which you see projecting from its snout, it conveyed its food to its mouth. Dr. Buckland also suggests that it probably used its tusks to hook fast to the bank of the lake or river, to keep its head out of water during sleep, while the rest of its body floated in the stream.
Besides this and many other creatures whose genera and species afterward totally disappeared, several animals existed in the same general period which have their representatives now upon the earth—such as the tapir, the ape, the rhinoceros, the hog, the cat, the hippopotamus, the horse, &c. The mastodon, an animal resembling the living elephant, but much larger, also lived in those times, but afterward died out, with others.
In strata a little newer than these, there have been found the remains of another gigantic creature, called the Megatherium, which signifies great beast. The bones of this quadruped have been found in the extensive tertiary plains and pampas of South America, and a skeleton of it has been reconstructed and placed in the museum at Madrid, in Spain.
It is described as larger than the rhinoceros, and possessing characters which allied it both to the sloth and the ant-eater. Its body, exclusive of the tail, was about twelve feet long and eight feet high, and of great thickness. The bone of its thigh was nearly three times as thick as that of the elephant, and it measured five feet across the haunches. Its fore-feet were a yard in length, terminated by enormous claws, enabling it to dig into the earth and tear up the roots of trees and plants, which seem, by the form of its teeth, to have constituted its chief article of food.
The skeleton of this creature is represented in the following cut; and by imagining this to be clothed with flesh, you may have some idea of the general form and proportions of this huge inhabitant of the ancient world, which, like most of the creatures of those early periods, ceased to exist long before man came into being.
In these strata, and in those subsequently formed, we find not only the remains of several other animals, of which there are now no living representatives, but also the remains of the elephant, ox, deer, hyena, bear, monkey, &c. And the higher we ascend in the strata, the more nearly do the remains, not only of land but also of sea animals, and of plants, resemble species now existing upon the earth.
Sir Charles Lyell informs us that, in the older tertiary strata, the species of shell-fish that have continued their existence to this time, bear the proportion of only about five to one hundred of those which, since that period, have died out; while in the newer tertiary deposits the proportions are reversed, and about ninety-five existing species are found to only five that have since died out.
Thus have we seen, in the course of this and preceding letters, that from the earliest times there has been a gradual progression, both of inorganic and organic nature, toward the physical conditions, and the races of plants and animals, now in existence, until there was an actual “shading off” into the conditions and living beings of the present geological era.
The changes which from the infancy of our globe have progressively gone forward in the different branches of creation, have been always mutually suited to each other, and each age has been furnished with just such living forms in the vegetable and animal kingdoms as were best adapted to the then existing state of earth, water, air, and the heat and light of the sun. Thus the all-wise and bountiful Creator has suffered no habitable condition of the globe to lie unoccupied by beings capable of happiness, and has displayed His wisdom and goodness in every scene of this sublime drama of creation!
I wish now to impress more deeply upon your minds a remarkable fact, which we have before but incidentally intimated. It is, that throughout all these vast groups of deposits, abounding with the remains of other animals, not the slightest trace of the remains of man, or any of his works, have been found! Neither his bones, his utensils, his weapons, or any thing which indicates his presence, have yet been discovered in any formations, except those of the most recent date, and of a kind now going on. The creation of man was reserved for the last and crowning act of Divine skill and goodness.
During untold and inconceivable periods, tribe after tribe of fishes had sported in the briny deep, huge reptiles had lurked in the swamps and marshes, and fearful quadrupeds had prowled through the dismal forests; but the sound of the woodman’s ax, the dashing of the hunter’s steed, and the hum of the crowded city, were not yet heard. No burning incense rose to heaven, and no altar yet smoked with sacrifices to the Creator of all. Man did not yet exist!
From the earliest ages, when poisonous vapors loaded the air, and by obscuring the sun spread “darkness over the face of the deep,” Nature had been gradually approaching to those conditions suitable to the introduction of man; and these progressive changes were brought to a completion by the diluvial revolution which immediately followed the close of the Tertiary Period. The earth was then, as before intimated, for a long time overflown by seas, on whose bosoms floated immense icebergs, which, sinking beneath the surface, would often strike and rub violently along over the ground which then constituted the sea bottom. By this means hills and sharp projections of rock were ground down, deep hollows were filled up, the quantity of soil was greatly increased, and the earth was every way better fitted for the reception of man.
Accordingly, at the close of this period, when the waters had subsided, and all things were in readiness, man was created, in God’s own moral image, as the crowning excellency of all the Creator’s works; a being distinguished from all other earthly creatures by the capacity of knowing and adoring the Author of his existence, and of ruling, by his intelligence, the inferior orders of living beings.
I have thus, my young friends, fulfilled my intention to give you a general view of the progress and order of the creative changes through which our globe and its living inhabitants have passed, from the time when the Spirit of the Creator first “breathed upon the face of the waters to the present period. For a more detailed unfolding of this highly interesting subject, I must refer you to the writings of Lyell, Bakewell, Buckland, Mantell, Hitchcock, and others; and I hope you will not neglect such observations of nature as you may be able to make.
One more point, and I have done. In following me through these descriptions, you can not have failed to be impressed with the immense periods of time which must necessarily have been consumed during the progress of the changes that have been mentioned; and many of you have doubtless inquired, “How is it, then, that the Bible says that creation was accomplished in six days?”
My young friends, creation was accomplished in six days, as geology itself clearly and distinctly proves. But those days were God’s days, not man’s; and we are, in general terms, distinctly told in the Bible, that “one day with the Lord is as a thousand years, and a thousand years as one day.” A great many examples might be produced from different portions of the Bible, in which the word “day” is manifestly used for a very long though indefinite period of time; and in one instance this whole history of creation is comprehended in one day. (See Gen. ii. 4.)
With this interpretation of the word “day,” geology may be considered as demonstrating the Bible history of creation to be true; for the record of creation’s successive stages, as found respectively in the rocks and the Bible, are found to exactly correspond in all essential particulars. This I have endeavored to show in another work: and expressing my deep conviction that all the revelations of true science will only tend to confirm the essential teachings of that Sacred Book, when properly interpreted, and hoping that you will all endeavor to profit, physically, intellectually, and morally, by the suggestions and statements which have been laid before you in these letters, I now bid you an affectionate FAREWELL!