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Show 28 THE EARTH FORMED. settlement of the earth in its :present form. They are in deed of an order of events which we see going on, under the agency of more or less intelligible causes, even down to the present day. We n1ay therefore consider them generally as comparatively rect>nt transactions. Abstracting them from the investigations before us, we arrive at the Idea of the earth in its first condition as a globe of its pre· sent size-nan1ely, as a mass, externally at least, consist. ing of the crystalline kind of •·ock, with the waters of the present seas and the present atmosphere around it, though these 'vere probably in considerably different conditions, both as to temperature and their constituent materials from what they now are. We are thus to presume that that crystalline texture of rock which we see exemplified in granite is the condition into which the great bulk of the solids of our earth were agglomerated directly from the nebulous or vaporiform state. It is a condition eminently of combination, for such rock is invariably composed of two or more of four substances-silica, mica, quartz and hornblende-which associate in it in the form of grains or crystals, and which are themselves each composed of a group of the ~imple or elementary substances. Judging from the rP.sults and from still remaining- conditions, we must suppose that the heat retained in the interior of the globe was more intense, or had greater freedom to act in some places than in others. These became the scenes of volcanic operations, and in time marked their situations by the extrusion of traps and basalts from below-namely, rocks composed of the crystalline matter fused by intense heat, and developed on the surface in various conditions, according to the partiular circumstan· ces under which it was sent up ; some, for example, be· ing thrown up under water, and some in the open air, which conditions are found to have made considerable difference in its texture and appearance. The great stores ot· subterranean heat also served an important purpose in the formation of the aqueous rocks. These rocks might, according to Sir John Herschel, become subject to heat in the following manner;-While the surface of a particular mass of rock forms the bed of the sea, the heat is kept at a ~ertain distance from that surface by the contact of the 'vater; philosophically speaking, it radiates away the heat into the sea, and (to resort to common language) is t'ooled a good way down. But when new sediment set .. I • ERA OF THE PRIMAR "1 ROCX.S. tles at the bottom of that sea, the heat rises up to what wa~ forme.rly t_he surfac~; and .when a second quantity of sedunent Is latd down, It continues to rise throucrh the first of the deposits, which then becomes subJected· to ~hose cha~ges w~ich heat is calculated to produce. T.h.Is process Is precisely the same ai that of putting ad~ hbonal coats upon our own bodies; when, of course, the 1nt~rn~~ heat ris~s throug~ each coat in succession, and the thud (supposing there IS a fourth above it) becomes as warm as. perhaps ~he first originally was. I!! _spe~lnng of ~edimentary rocks, we may be said to be anhc1pahng. It Is necessary, first, to show how such rocks 'vere formed, or how stratification commenced Geol?gy tells us as plainly as possible that the original crystalline mas~ was not 3: perfectly smooth ball, with air a_nd ~ater playing round It. There were vast irregularities In t~e surface-irregularities trifling, perhaps, compared Wit~ the w~ole bulk o~ the globe,, but assuredly vast ~n comp~r~son ~~ th any whi?h now exist upon it. These ll'regularihes might be occasioned by inequalities in the C?ollng of the substance, or by accidental and local sluggishness ~f the materials, or by local effects of the concen~ rated 1nte~nal heat. From -yv~atever c~use they arose, th_el e they we~ e, enormous gran I he mountains, intespersed With s~as which sunk to a depth equally profound, and ~y whiCh, perhaps, th~ ~oun~ains were wholly or parha. lly_covered. Now, It Is a fact of which the very first pnnc1ples of geology assure us, that the solids of the globe cannot fo.r a moment ~e exposed to water, or to the atmoshhe_ re, Without becoming liable to change. They instantly egin to wea~ down. This operation, we may be assured, proceeded With as 1nuch certainty in the earliest aO'es of ou1~ e~rth's history, as it do.es now, but upon a muchb more maontficent scale. There IS the clearest evidence that the ~eas of thos.e days were not in some instances less than a .. undred miles I? depth, however much more. The subaqueous m~untains must necessarily have been of at least equal magnit~d~ .. The system of disintegration consequent up~n such c.ondihon~ W?uld be enormous. The matters worn off, be.Ing earned Into the neighboring depths, and ther~ deposited, became the components of the earliest str~hfieti rocks, the first se~ies of which is the Gneiss and Mtea Sla~e S'!!sten~, or senes, exa1nples of which are exposed to VIew In the Highlands of Scotland and in the |