which the whole of the stratified rocks were to be built, was being laid down. The serene aspect of the surface at this late period of its history-our own time-suggests nothing of the turbulence and unrest which accompanied the gathering together of the constituents of a granitic rock when the earth was young.

Geology would be a worthless and totally uninteresting study were we compelled thus to rest upon conjecture in all cases, and had we nothing more tangible than speculations on the origin of a rock composed of crystals of quartz, mica, and felspar, or that of a half-baked limestone. From the moment, however, when water began to deposit fragments of the older rocks as a sediment in seas, lakes, and rivers, the evidence becomes clear, and leads to conclusions of the highest interest, which can be verified at every step.

CHAPTER III.

THE STRATIFIED FORMATIONS.

The stratified rocks, their origin, structure, and characters-The process of stratification in rivers and lakes-The Rhone and Lake of Geneva -The Amazon--Oceanic tides, currents, etc., agents in stratification-Deep-sea deposits-Clay and chalk in the Atlantic and Pacific Oceans-Table of stratified formations-Examples of thickness of strata-Breaks in the succession and “unconformability" of rocks -Chemical action.

THE term "stratified," applied to the second leading division of rocks, sufficiently indicates that they have been spread out by the action of water, whether the immediate agent was an ocean, a lake, a river, a glacier, an iceberg, or the gently disintegrating force of rain. As soon as the earth had cooled sufficiently to permit condensation to take place in the watery vapour surrounding it, the ceaseless wear and tear of the surface, which has accumulated so vast a mass of material, began. From the dense canopy of vapour hanging over the earth -through which the light of the sun did not penetrate perhaps for long ages-were poured volumes of water, in comparison with which our heaviest rainfall is a mere drizzle; and this continued without intermission, until permanent terrestrial reservoirs and lines of drainage

into them had become established, and the new order of geological action-stratification-which was destined henceforth to determine the contour of the surface and provide the conditions of life, came into operation.

Our only guide to a knowledge of the past is observation of the present; but believing, as we are justified, in the uniformity of natural laws, we may fairly employ a comparison with existing phenomena in the interpretation of the past, with some allowances for greater local or general intensity of action. Every appearance presented by a stratified rock can be fully explained and verified by reference to examples under our own eyes; excepting some chemical modifications of the materials, due probably to the long lapse of time and the influence of contact with heated masses under pressure during the progress of stratification, or after its completion. The mechanical structure is, however, the more important, and generally indicates, without doubt, whether the rock was accumulated by an ocean, or river, or by glacier or berg ice, independently of the very valuable evidence derived from the vegetable and animal remains often included in it.

Catastrophic explanations of geological change find little favour now among geologists; but until a more thorough examination of the stratified rocks was made, these were the prevailing views. The oldest theological creeds and philosophical systems assumed the existence of periodical convulsions, and intervals of destruction and reconstruction, attributing them often to supernatural causes. Neither was this unreasonable in the then

imperfect state of knowledge. It was inconceivable that a mighty mountain chain could have been raised by the exceedingly gradual force which we now know has in most cases sufficed; and the power of the Titans was invoked to account for it. The older philosophers were misled by violent local action—the eruption of a volcano or the shock of an earthquake-into the belief that all the grander results of distribution of land and water and alternations of level were produced by similar convulsions on a still larger scale. Thus the earlier geologists were partly under the influence of ancient philosophies, when they devoted themselves to the task of interpreting phenomena never until this century investigated by any strict scientific methods; although it would seem that they should have challenged attention and compelled inquiry no less urgently than the constitution of the celestial bodies.

Though, then, we must no longer attribute the major changes of level to violent disturbance, convulsions have undoubtedly taken place over considerable areas in remote times, and most probably on a more energetic scale than any of which we have present experience; nevertheless the cardinal fact remains that lakes and river valleys have been excavated, and table-lands and mountains formed, by forces operating with remarkable uniformity, regularity, and slowness, while preserving often the minutest structures of plants and animals uninjured. Periods of widely extended and violent disruption passed away with the consolidation of the earlier unstratified rocks, and water took the place of fire in the

new order of things, by which their seamed and scarred lineaments were to be moulded anew, and a totally different and more tranquil aspect impressed upon the terrestrial features.

A stratified rock may be described as an aggregation, more or less compact, of particles separated from a number of others, deposited in layers, and consolidated by pressure, assisted frequently by lime, iron, or silica, as a cement. The particles may be angular or rounded, or a mixture of both. In the sandstones they are composed mostly of rounded grains of quartz and silica; in the limestones, of carbonate of lime; in the slates and shales, of fine mud; in the conglomerates, of rounded, water-worn pebbles, cemented together with finer material; and in the coal rocks, of densely impacted vegetable matter. The colour frequently depends upon the presence of iron in some form, of lime, or the special prevailing tint of the rock from which the particles were originally derived. The coarser the texture of the rock, the more probable it is that it has been deposited by rapidly moving, shallow water; while the fine slates and chalks have been laid down in still, and often deep water at 2000 feet below the surface of ocean or lake. This we can prove by a simple experiment. Take a handful of coarse silt from the roadside, and throw it into a tumbler of water. The larger particles fall to the bottom, while the smaller remain in suspension some time, rendering the water turbid, until they also eventually settle and become a finer sediment, lying upon the coarser beneath; and the result is two strata, not defined by any