GEOLOGY.

ACTION OF WATER ON STONE.

ALL detached pieces and fragments of stone or rock, whether they be boulders of many tons weight, or pebbles, or sand, or clay, or mud, have once formed portions of large, solid, originally constituted masses of rock, and have all, with the exception of matters actually blown from the crater of a volcano, acquired their present form and condition through the action of flowing water

There

is not a shower of rain that falls, whether on the crowded street, the dusty road, the plains, the hills, or the mountain summits, that does not cause a multitude of rills and streams of muddy water to flow from higher to lower levels. The mud borne along by that water was once part of a solid rock... Even if it be but the waste of the bricks and tiles of our houses, this is still true; and it is equally true for every other case, except for those particles of it that may be the result of the decomposition of animal or vegetable matter... Even the gentlest rain that soaks silently into the most richly carpeted meadow of grass, contributes to the stock of water contained below ground, which here and there bursts forth in springs, carrying momently some grain of mineral matter to the brook, the river, and the ocean... Who has not seen the springs discolored after heavy rain? Who has not watched in wet weather the swollen brook or the roaring mountain-torrent, with its thick, muddy, coffee-coloured water? Who does not know the flooded aspect of a river, with its dull, yellow, turbid eddies, so different from the limpid stream that commonly flows between its banks?... Whoever has seen these things, has seen one of the multitudinous actions of nature which are for ever and everywhere in operation, performing slowly, and in the lapse of ages, mighty works by means apparently inadequate, and at first sight, perhaps, not especially adapted to the purpose. There are, however, other agencies acting with greater local power than mere rain, in wearing away solid rocks and transporting the waste to other localities. We have alluded to the

action of brooks and rivers; but if we were to trace them more minutely and in detail, and follow them up to where they acquire a swifter stream, or where rapids and cataracts occur in them, we should estimate still more highly their destructive power on solid rock... Rivers are in fact great natural saws or planes, for ever grooving furrows in the land. Let any one look at the bed of a mountain torrent, where it has found its path through a deep ravine, and he will see the amount of its force perpetually acting through uncounted ages..." The rocks," says Lyell, "over which the Niagara water flows, project, and sometimes fall in enormous fragments, with a noise like distant thunder. The width of the river below the falls is reduced to a hundred and sixty yards, and it runs furiously along the walled valley, cut by the stream, in a bed covered with masses of rock. By the continued destruction of the rocks the falls have, within the last forty years, receded nearly fifty yards; and it is supposed, with reason, that the cataract was once as low as Queenstown, seven miles from its present situation."

On mountain-tops, or in high latitudes, even on lower ground, frost is a great agent of degradation. Any one who ascends the mountains of our own islands for the first time, will often be surprised at the multitude of angular fragments and fallen blocks he sees scattered over their summits, or piled at the foot of their precipices... Of these many, if not most, have been detached by the action of frost, causing the water contained in the joints and crevices to expand and rend them asunder, just as in a cold winter's night the jugs and water bottles are apt to be burst by, the frost in our bed-rooms... If we were to visit mountains such as the Alps, where glaciers are formed, we should see still another effect of frost. A glacier is in fact a stream of ice slowly descending the mountain-side. In its slow but mighty and irresistible progress, it exerts an enormous force in grinding and grooving the rocks on which it rests, tearing off many of the projecting blocks it meets with, and, by undermining the cliffs at its sides, causing blocks to fall upon its surface. These blocks it constantly carries forward, till it comes to the boundary, where it melts away, when it of course deposits them. They there form a huge mound or ridge of broken fragments, called in the Alps a "moraine."

Similarly in all those countries where ice forms periodically in large quantity, either on the rivers or on the sea-shores, it both rends asunder and grinds up whatever rock it comes in contact with, but more especially in these cases does it aid in carrying off to distant localities blocks already detached... It encases these in its own mass, freezes them in, and when it is

itself floated off, bears them along with it, transporting them perhaps many miles, or, in the case of icebergs, even many hundred miles from the place where it found them, and, on melting, drops them at the bottom of the sea.

Of all agencies, however, the most efficient in the destruction and degradation of rock, because it is both locally powerful and very widely diffused, is the action of the sea-breakers. In all climes, in all latitudes, along all shores of all seas and oceans, this action is ceaselessly at work: day and night, summer and winter, gently and imperceptibly even in calms, furiously and vigorously in storms, gradually but steadily in moderate weather, wave after wave is launched from the sea against the land, eating and tearing it away. J. Beete Jukes.

SCULPTURE OF MOUNTAINS.

Ir is evident that, through all mountain ruins, some traces must still exist of the original contours. The directions in which the mass gives way must have been dictated by the dispositions of its ancient sides; and the currents of the streams that wear its flanks must still, in great part, follow the course of the primal valleys. So that, in the actual form of any mountain peak, there must usually be traceable the shadow or skeleton of its former self; like the obscure indications of the first frame of a war-worn tower, preserved, in some places, under the heap of its ruins, in others, to be restored in imagination from the thin remnants of its tottering shell; while here and there, in some sheltered spot, a few unfallen stones retain their gothic sculpture, and a few touches of the chisel, or stains of color, inform us of the whole mind and perfect skill of the old designer... With this great difference, nevertheless, that in the human architecture, the builder did not calculate upon ruin, nor appoint the course of impending desolation; but that in the hand of the great Architect of the mountains, time and decay are as much the instruments of His purpose as the forces by which He first led forth the troops of hills in leaping flocks;—the lightning and the torrent, and the wasting and weariness of innumerable ages, all bear their part in the working out of one consistent plan; and the Builder of the temple for ever stands beside His work, appointing the stone that is to fall, and the pillar that is to be abased, and guiding all the seeming wildness of chance and change, into ordained splendors and foreseen harmonies. How the top of the hill was first shaped so as to let the

currents of water act upon it in so varied a way we know not... A stream receives a slight impulse this way or that, at the top of the hill, but increases in energy and sweep as it descends, gathering into itself others from its sides, and uniting their power with its own. A single knot of quartz occurring in a flake of slate at the crest of the ridge may alter the entire destinies of the mountain form... It may turn the little rivulet of water to the right or left, and that little turn will be to the future direction of the gathering stream what the touch of a finger on the barrel of a rifle would be to the direction of the bullet. Each succeeding year increases the importance of every determined form, and arranges in masses yet more and more harmonious, the promontories shaped by the sweeping of the eternal waterfalls.

The importance of the results thus obtained by the slightest change of direction in the infant streamlets, furnishes an interesting type of the formation of human characters by habit. Every one of those notable ravines and crags is the expression, not of any sudden violence done to the mountain, but of its little habits, persisted in continually. It was created with one ruling instinct; but its destiny depended nevertheless, for effective result, on the direction of the small and all but invisible tricklings of water, in which the first shower of rain found its way down its sides... The feeblest, most insensible oozings of the drops of dew among its dust were in reality arbiters of its eternal form; commissioned with a touch more tender than that of a child's finger, as silent and slight as the fall of a halfchecked tear on a maiden's cheek, to fix for ever the forms of peak and precipice, and hew those leagues of lofted granite into the shapes that were to divide the earth and its kingdoms. Once the little stone evaded,—once the dim furrow traced,—and the peak was for ever invested with its majesty, the ravine for ever doomed to its degradation... Thenceforward, day by day, the subtle habit gained in power; the evaded stone was left with wider basement; the chosen furrow deepened with swiftersliding wave; repentance and arrest were alike impossible, and hour after hour saw written in larger and rockier characters upon the sky, the history of the choice that had been directed by a drop of rain, and of the balance that had been turned by a grain of sand. Ruskin.

ROCKS MECHANICALLY AND CHEMICALLY FORMED.

ALL sand being composed of the small fragments of preexisting rock, rounded by the action of moving water, we are obliged to conclude that all sandstone is composed of fragments of pre-existing rock, rounded by the action of moving water, deposited at the bottom of that water, and subsequently compacted together into stone or rock... It is, therefore, tolerably certain that all the waste of rock which is caused by the moving waters of brooks, rivers, lakes, and seas, is eventually deposited in their deeper and stiller portions, where it is gradually formed into these kinds of rock... We must feel pretty sure also that in all our present lakes and seas, without exception, there is constantly taking place, in one part or other, a deposition of such materials, which, when accumulated in any quantity, bed over bed, must be, by the mere weight and pressure of the superincumbent portions, compacted together into tolerably firm stone or rock. If we had any doubt on this point, we should not be able to continue our examination of such rocks very long without having those doubts removed, by discovering in them the remains of animals and plants that had lived in or had been carried into the waters.

We should find in some sandstones huge stems of trees, more or less completely converted into stone, in some cases changed into the purest flint, in others converted into lignite or into coal. In some sandstones, and in many shales, we should find the leaves and stems of plants, with all their delicate tracery exquisitely preserved... In many rocks, whether sandy or clayey, we should find either the entire bodies or the casts of shells, crabs, corallines, seaweeds, and other aquatic beings, often occurring in regular beds, and under such circumstances as prove them to have lived and died in the place we now find them, when that place was covered with the waters of lakes and seas... We find also the skeletons of fish, reptiles, birds, and quadrupeds,-bones either of animals that lived in the waters, or of carcases that have been carried into them from the land by the action of rivers.

If we required any other evidence, then, than the mere structure of the rock, to prove that all the rocks of which we have been speaking, such as sandstone and conglomerate, shale, slate, and the various forms of clay, were formed by the slow and gradual accumulation of earthy matters under water, we should have in these facts abundant proof of the position... Now, to rocks formed by such agency we may rightly assign the