An Expository Outline of the "Vestiges of the Natural History of Creation" / With a Notice of the Author's "Explanations:" A Sequel to the Vestiges

by S. Laing

DEPOSITS OR ROCK FORMATIONS.

The first of the series is the Gneis and Mica Slate System, of which examples are exposed to view in the Highlands of Scotland and the west of England. These earliest stratified rocks contain no matters which are not to be found in the primitive granite. They are the same in material—silica, mica, quartz, or hornblende—but changed into new forms and combinations, and hence called by Mr. LYELL metamorphic rocks. Some of them are composed exclusively of one of the materials of granite; the mica schist, for example, of mica; the quartz rocks, of quartz. In the metamorphic rocks no organic remains have been found, and they are geologically below all the rocks that do contain traces of animal life.

From the primary rocks we pass into the next ascending series, called the Clay Slate and Grauwacke Slate System, which in some places is found resting immediately on the granite, the antecedent bed being there wanting. This deposit has been well examined, because some of its slate beds have been extensively quarried for domestic purposes. By some geologists it is called the Silurian System, it being largely developed at the surface of a district of western England formerly occupied by the Silures. It is found also in North Wales and in the north of England, in beds of great thickness, and in Scotland, but there the Silurian rocks are more feebly represented.

The Old Red Sandstone, or Devonian System, comes next. It forms the material of the grand and rugged mountains which fringe many parts of our Highland coasts, and ranges, on the south flank of the Grampians, from the eastern to the western sea of Scotland. There is no part of geology and science more clear than that which refers to the ages of mountains. It is as certain that the Grampian mountains are older than the Alps and Apennines, as it is that civilisation had reached Italy and enabled her to subdue the world, while Scotland was the abode of barbarism. The Pyrenees, Carpathians, and other ranges of continental Europe are all younger than these Scotch hills, or even the insignificant Mendip Hills of southern England. Stratification tells this tale as plainly, and more truly, than LIVY tells the story of the Roman republic. It tells us that at the time when the Grampians sent streams and detritus to straits where now the valleys of the Forth and Clyde meet, the greater part of Europe was a wide ocean.

The last three series of strata contain the remains of the earliest occupants of the globe, and of which we shall soon speak. They are of enormous thickness—in England, not much less than 30,000 feet, or nearly six miles.

We have now arrived at the secondary rocks, of which the lowest group is the Carboniferous Formation, so called from its remarkable feature of numerous interspersed beds of coal. It commences with beds of the mountain limestone, which in England attains a depth of 800 yards. Coal is altogether composed of the matter of a terrestrial vegetation, transmuted by putrefaction of a peculiar kind beneath the surface of water, and in the absence of air. From examples seen at the present day at the mouths of such rivers as the Mississippi, which traverse extensive sylvan regions, it is thought that the vegetation, the rubbish of decayed forests, was carried by rivers into estuaries, and there accumulated into vast natural rafts, until it sank to the bottom, where an overlayer of sand or mud would prepare it for becoming a stratum of coal. Others conceive that the vegetation first went into the condition of peat moss, that a sink in a level then exposed it to be overrun by the sea and covered with a layer of sand or mud; that a subsequent uprise made the mud dry land, and fitted it to bear a new forest, which afterwards, like its predecessors, became a bed of peat—that, in short, by repetitions of this process the alternate layers of coal, sand and shell constituting the carboniferous group were formed.

The Magnesian Limestone deposits succeed the carboniferous, and sometimes pass into them by insensible gradations. In the south of England they are represented by conglomerates, and partly composed of the solid and more or less rounded fragments of the older strata. They afford a proof of what geologists have often occasion to remark of the long periods of time during which the ancient works of nature were perfected; for the older rocks were solid as they are now, and their organic remains petrified at the time these conglomerates were forming.

We can only briefly glance at the remaining chapters of geological history. The New Red Sandstone forms the base of the great central plains of England, and is surmounted by the oliferous marls and red arenaceous beds which pass under the succession of great oolitic terraces that stretch across England from the coasts of Dorsetshire to the north-eastern coast of Yorkshire. It marks the commencement of an important era, being the strata in which land animals are first found. The Oolte System which follows marks the beginning of mammalia, and in some of its beds in Buckinghamshire are found the exuviæ of tropical trees. Near Weymouth, in the well-known dirt beds, are found trees with their silicified trunks growing up in the position of nature, and their roots embedded in the soil on which they grew.

Next we have the chalk or Cretaceous Formation, that makes such a conspicuous figure in England. The celebrated cliffs of Dover are of this era. It forms a stripe from Yorkshire to Kent, and is found in France, Germany, Russia, and in North America. The English chalk beds are 1,200 feet thick, showing the considerable depth of the ocean in which they were formed. Their origin has been a questionable topic; they were thought to be formed from the detritus of coral reefs, but Professor EHRENBERG has recently announced, as the result of his microscopical researches, that chalk is composed partly of inorganic particles and partly of shells of inconceivable minuteness, a cubic inch of the substance containing about ten millions of them.

In the hollows of the chalk-beds have been formed series of strata—clay, limestone, marl alternating—to which the name of the Tertiary System has been given. It is irregularly distributed over vast surfaces of all our continents, and must be considered as the beds of estuaries left at the conclusion of the cretaceous period. London and Paris rest on basins of this formation, and another such basin extends from near Winchester under Southampton, and reappears in the Isle of Wight.

We hasten upward to the Diluvial System, which brings us near to the present surface. To this era is referred the erratic blocks, or gigantic boulder stones, which have been driven by floods across our continents, or drifted in icebergs over valleys, and perched sometimes on mountain tops. To it also must be referred the till of Scotland and the great brown clay of England, and our vast beds of gravel and superficial rubbish, connected with the deluvium in the history of ossiferous caverns, of which that examined by Dr. BUCKLAND at Kirkdale is an example. They occur in the calcareous strata, as the great caverns generally do, and have in all instances been naturally closed up till the period of their discovery. At Kirkdale the remains of twenty-four species of animals were found—namely, pigeon, lark, raven, duck, partridge, mouse, water-rat, rabbit, hare, hippopotamus, rhinoceros, elephant, weasel, fox, wolf, deer, ox, horse, bear, tiger, hyena. From many of the bones of the gentler of these animals being found in a broken state, it is supposed that the cave was the haunt of hyenas and other predaceous animals, by which the smaller ones had been consumed.

We come last to the Modern or Superficial Formation, of which the best specimen is the great Bedford level, that spreads over the lower lands of Norfolk, Cambridgeshire, and Lincolnshire, consisting of accumulations of silt, drifted matter, and bog-earth, some of which began before the earliest periods of British history. When these accumulations are removed by artificial means, we find below sometimes shells of recent species, and the remains of an old estuary, sometimes sand-banks, gravel beds, stumps of trees, and masses of drifted wood. On this recent surface are found skulls of a living species of European bear, skeletons of the Arctic wolf, European beaver and wild boar, and numerous horns and bones of the roebuck and red deer, and of the gigantic stag or Irish elk. They testify to a zoology on the verge of that now prevailing or melting into it. In corresponding deposits of North America are found remains of the mammoth, mastadon, buffalo, and other animals of extinct or living species.

Considering it best not to interrupt the description of the successive formations, this is almost the only allusion that has been made to the fossils which constitute so important a part of geological science. It is now to be explained that from an early period, that is, from the metamorphic deposit to the close of the rock series, each formation is found to enclose remains of the organic beings, plants, and animals, which flourished upon earth during the time they were forming; and these organisms, or such parts of them as were of sufficient solidity, have been in many instances preserved with the utmost fidelity, although for the most part converted into the substance of the enclosing mineral. The rocks may be thus said to form a kind of history of the organic departments of nature apparently from near their beginning to the present time. It is upon the commencement and progress of life under these circumstances that the author of the Vestiges of Creation has put forth some of his most startling and controversial propositions; but before noticing them it will be useful to prepare the way by shortly describing the gradations of organic existences, following the same order as observed in the rock series, by beginning with the lowest or humblest forms of organization.