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BRITISH STRATIFIED SYSTEMS,
TO WHICH THE FOLLOWING SKETCHES MORE ESPECIALLY REFER.
The subjoined tabulation exhibits the arrangement of the British stratified rocks, as accepted by our leading geologists-minor and local deviations of superposition being subordinated for the sake of distinct comprehension and ready reference : Systems.
Pleistocene. · CAINOZOIC.
| Lower New Red Sandstone.
Red Sandstones, Conglom-
erates, and Cornstones.
l and Conglomerates.
| Limestones, Slates, Grits.
RANGE OF TRAPPEAN ROCKS.
ORDER AND SUCCESSION OF LIFE,
ESPECIALLY AS REFERRED TO IN THE FOLLOWING SKETCHES.
The subjoined tabulation exhibits proximately the stages at which the great ascending sections of Plants and Animals make their first appearance in the stratified systems :
| Man. Plants and animals of
existing species and distribu-
and animals of existing or-
reptiles, fishes, shell - fish,
tiles, fishes, shell-fish, crus-
tacea, zoophytes ; conifere,
zoophytes ; ferns, lycopods,
tracks, zoophytes; sea-weeds. 18
RANGE OF ENDOGENS. RANGE OF VERTEBRATA.
RANGE OF GYMNOGENS.
RANGE OF ACROGENS.
CHIPS AND CHAPTERS.
GEOLOGY-ITS AIM AND OBJECTS.
In the study of any department of science, it is of the utmost importance to have, at the outset, some notion of its aim, scope, and bearing. Knowing its aim, the student can direct his attention more exclusively-understanding its scope, he is restrained from unwarranted speculationand being aware of its bearings, he can the more readily direct them to their legitimate purpose. No mere definition, however explicitly expressed, can convey a satisfactory idea of all that any science is and aims at; hence the necessity for a good deal of preliminary and circumlocutionary explanation. It is to this sort of explanation we devote the present chapter, that the reader may have a clear conception of what Geology really is, and at what, as an inductive science, it may be fairly anticipated to arrive.
With the word Geology the youngest pupil at once associates something concerning rocks and minerals and the structure of the earth. The science, however, has much more to do than merely describe the rocks and minerals that compose the stony crust. These rocks, subjected to
the operation of certain forces, are in a state of incessant waste and reconstruction. Winds, frosts, rains—springs, streams, rivers—waves, tides, and ocean-currents, are continually wearing and wasting in one district, and as incessantly laying down the abraded material in newer arrangements in another. What is worn from the hills and high grounds by the frosts and rains and runnels is carried down by the rivers and deposited in the valleys, lakes, and estuaries, or borne out to the ocean ; and what is washed by the waves from the headlands and sea-cliffs is swept by the tides and currents to seaward depths or to sheltered bays and recesses. And while all this and the growth of peat-mosses, shell-beds, and coral-reefs are going on from without, the fire-forces from within are as incessantly upheaving or depressing—forming new hills by volcanic eruption, or producing new irregularities of surface by earthquake convulsion. In this way former rocks are worn away and new ones constructed, old lands submerged and new ones upheaved, and the distribution of sea and land, at every change, more or less affected.
Nor is it to mere physical and mechanical changes alone that the earth is subjected ; every new distribution of sea and land, every elevation of terrestrial surface or deepening of sea-bed, is necessarily accompanied by some change in climate and condition, and consequently by a corresponding change in its vegetable and animal productions. In fine, under the operation of the forces to which we have alluded, the whole physical geography of the globe is in a state of slow but unceasing change; and as these forces are permanent and enduring as the universe itself, changes must have taken place in time past similar to those that are now taking place around us. There can be no waste save from pre-existing rocks; the earliest stratified formation in the earth's crust proclaims by its structure and arrangement that it is but the waste and debris of some other rockformation that preceded it. And further, as the forces that now act leave record of their operations in the rocks they produce, so the older rocks contain the history of the manner in which they were formed and of the conditions under which they were aggregated. To study the rocks of the earth's crust and the history they contain, from the most recent and superficial to the oldest and deepest we can reach, is the prime aim of geology; and the more thorough our knowledge of existing conditions and operations, the more perfect will be the interpretation. In other words, the more we know of the physical geography of the present day, of the forces that act and the results they produce, of the plants and animals that live, and the mode in which they are entombed in the rocks, the better will we be enabled to infer from our examination of the old rocks the mode in which they were formed, the distribution of sea and land at the time of their formation, and the conditions under which their imbedded plants and animals existed.
The aim of geology is therefore to read, through its rocks and fossils, the history of the earth's crust and the changes it has undergone. We see at the present day how sedimentary or stratified rocks are formed in lakes, in seas, and in estuaries, through and by the agency of water, and we therefore infer that all stratified rocks in the crust have been produced in a similar way. We see sands and gravels laid down along shore, and muds and marls in deeper water, and therefore conclude that all rocks of similar composition and structure have been formed in similar positions. We know that the plants and animals of the land and the lake differ from those of the sea, and that those of the estuary, again, differ from both ; and so, when examining the fossil plants and animals (the flora and