of opinion prevails among geologists as to the origin, classification, and the nomenclature by which the greater groups of rocks composing the earth's outer surface are to be designated; nevertheless, an accordance has been come to as regards the unstratified amorphous masses, in contradistinction to all the stratified ones of every denomination.

"That they also concur in considering the primary rocks, besides being deficient in organic remains, to be more compact and crystalline in texture than the others, and generally more elevated in their positions. That they appear, in very many instances, to have been thrust up from beneath the strata, raising these up also, whether they have perforated or not wholly cut through them; in the former case remaining flanked by stratified masses, which repose upon them in evident inconformity."

What has just been said, will be sufficiently intelligible, without further illustration, to those who have paid any attention to geology; but, for the benefit of those who are not versed in that and kindred studies, we subjoin an occasional extract from some of the numerous authorities, to place the subject in a diversity of lights, in order that conviction may be more impressed upon the mind.

"Unstratified rocks"-Dr. M'Culloch observes-"have been produced from below the stratified. They are found below these, or above them, or intermixed in the form of masses, beds, and veins. The intermixture is attended by mechanical and chemical changes in the stratified rocks. They have been consolidated after fusion, and their structure is necessarily chemical."*

Sir H. de la Beche says

"Our knowledge of the structure of the earth's crust is far from extensive, and principally confined to certain portions of Europe. Still, however, a mass of information has gradually been collected tending to certain general and important conclusions, among which the principal are—' -That rocks may be divided into two great classes, the stratified and the unstratified; that of the former some contain organic remains, and others do not; and that the non-fossiliferous

* Geology, vol. i. pp. 12, 13.

stratified rocks, as a mass, occupy an inferior place to the fossiliferous strata (or those which contain organic remains), also taken as a mass."

66

In the accompanying table, rocks are first divided into Stratified and Unstratified, a natural division, or, at all events, one convenient for practical purposes, independent of the theoretical opinions that may be connected with either of these two great classes of rocks."

Although Mr. Lyell, extends these two divisions to four, yet they may, with perfect propriety, be classified comprehensively into stratified and unstratified. The following is the description which Mr. Lyell gives :

"I shall begin," says he, "by endeavouring briefly to explain to the student how all rocks which compose the earth's crust may be divided into four great classes, by reference to the different circumstances and causes by which they have been produced.

"The first two divisions, which will at once be understood as natural, are the aqueous and volcanic, or the products of watery, and those of igneous action at or near the surface.

"The aqueous rocks, sometimes called the sedimentary or fossiliferous, cover a larger part of the earth's surface than any others; and are stratified, or divided into distinct layers or strata. The term stratum means simply a bed, or anything spread out or strewed over a given surface, and we infer that these strata have been generally spread out by the action of water.

"The volcanic rocks are those which have been produced at or near the surface, whether in ancient or modern times, not by water, but by the action of fire or subterranean heat. These rocks are for the most part unstratified, and are devoid of fossils. They are more partially distributed than the aqueous formations, at least in respect to horizontal extension.

"But there are other two classes of rocks very distinct from either of those above alluded to, and which can neither be assimilated to deposits such as are accumulated in lakes or seas, nor to those generated by ordinary volcanic action. The members of both these divisions of rocks agree in being highly crystalline, and destitute of organic remains. The rocks of one division have been called plu

* Manual, pp. 34, 35.

tonic, comprehending all the granites and certain porphyries, which are nearly allied in some of their characters to volcanic formations. The members of the other class are stratified, and often slaty, and have been called by some the crystalline schists, in which group are included gneiss, micaceous schist (or mica-slate), hornblende schist, statuary marble, the finer kinds of roofing slate, and other rocks afterwards to be described.

"Hence there are four great classes of rocks considered in reference to their origin; the aqueous, the volcanic, the plutonic, and the metamorphic."*

Professor Phillips, when comprehensively classing the rocks of which the earth's crust is composed, says

"The arguments on which we rely for the proof of the sub-aqueous origin of all the stratified rocks may be thus summed up: "The stratified structure is that which is always assumed by successive depositions of sediments of water.

"The materials (clay, sand, limestone, &c.) composing the strata of the crust of the globe are exactly similar and in the same condition, or else very analogous to deposits now forming under water in various parts of the globe, and similarly associated.

"The organic contents of the rocks are such as admit of no other explanation, for they are mostly of marine or fresh water origin, and the few terrestrial reliquiae which occur in them show, by various circumstances, that they were drifted from the land or overwhelmed by the sea. By combining all these considerations, we arrive at the positive conclusion, that all the really stratified rocks are of aqueous origin. But when we turn to the unstratified rocks, the same conclusion does not apply. Independent of the universal want of this unequivocal mark of watery action, ... the following circumstances are decisive :

"The materials of which the rocks are composed, are neither similar to those now deposited by water, nor in a similar condition. They are not composed of sands, clays, or limestone, but of a variety of crystallized minerals.

"In these unstratified rocks, organic remains do not occur, and, from the whole evidence, no doubt remains of the igneous origin of the crystallized and other unstratified rocks."†

* Elements, pp. 4, 15, 16.

+ Treatise on Geology, pp. 55, 56.

And again—

"It is remarkable that the lowest of all the known systems of stratified deposits should be at once the most extensive, the most nearly universal, the most uniform in mineral character, the only one from which organic life appears to be totally excluded, and in which the character of mechanical aggregation is the most obscure.

"The primary strata rest on unstratified, generally granitic rocks, so situated as to cut off all possibility of observation at greater depths. This granitic floor-this universal crystalline basis to the stratified rocks appears in many instances to have undergone fusion since the deposition of strata upon it, for veins pass from it into the fissures of these rocks. . . It is enough for our present purpose that the general truth is recognised, that the stratified rocks, which are the products of water, rest universally on the unstratified crystalline rocks, which, through whatever previous condition their particles may have passed, have assumed their present characters from the agency of heat. Igneous rocks, then, rest below all the aqueous deposits."*

In corroboration of the foregoing position, with which it is intimately connected, we adduce what is stated in the twentysixth Theorem" That the granitic, trappean, serpentinous, and porphyritic descriptions of amorphous rocks generally constitute the nucleii or centres of mountain ranges, and together with their recumbent strata attain the greatest elevations throughout the world. And that conjointly they occupy a considerable portion of its terrestrial surface."

The following we offer as some of its evidences :-
Professor Phillips says—

"The high mountain districts generally exhibit in the central points, or along their axes, granitic and other unstratified rocks under all their strata, which slope away on all sides at high angles of inclination, descend to lower and still lower ground, and, finally, pass under the plains and more level regions, and are there covered up and buried under other superimposed strata. Very few parts of the world offer real exceptions to this general statement.

*Treatise, pp. 94, 95, 69, 70.

And again

"This leads directly to another very important law of the phenomena of disturbed stratification. The centre or axis of the mountain group, and consequently of the disturbing movement, is generally seen to be a mass of unstratified rock, such as granite, sienite, &c., which shows, by a variety of circumstances, that it was not deposited in water, but rather crystallized from igneous fusion.'

The following extract is from the pen of the graphic writer on the Old Red Sandstone ::

"I have often stood," says Mr. Miller, "fronting the three Rossshire hills, Suil Veinn, Coul Beg, and Coul More, at sun-set in the fine summer evenings, when the clear light threw the shadows of their gigantic cone-like forms far over the lower tract, and lighted up the lines of their horizontal strata, till they showed like courses of masonry in a pyramid. They seem at such times as coloured by the geologist to distinguish them from the surrounding tract, and from the base on which they rest as on a common pedestal.

"The prevailing gneiss of the district reflects a cold-bluish hue, here and there speckled with white, where the weathered and lichened crags of intermingled quartz rock jut out on the hill sides from among the heath. The three huge pyramids, on the contrary, from the deep red of the stone, seem flaming in purple. There spreads all around a wild and desolate landscape of broken and scattered hills, separated by deep and gloomy ravines, that seem the rents and fissures of a planet in ruins, and that speak distinctly of a period of convulsion, when upheaving fires from the abyss, and ocean currents above, had contended in sublime antagonism, the one slowly elevating the entire tract, the other grinding it down, and sweeping it away."

"In most of our hills," he continues "the upheaving agency has been actively at work, and the space within is occupied by an immense nucleus of inferior rock, around which the upper formation is wrapped like a caul, just as the vegetable mould, or the diluvium wraps up this superior covering in turn. One of our best known Scottish mountains-the gigantic Ben Nevis-furnishes an admirable illustration of this latter construction of hill. It is composed of three cones or rings of rocks, the one rising out of or over the

*Treatise, pp. 42, 43, 61.