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old one that was passing away. But they too died and found a tomb beneath the waters; for Nature, with unexhausted energies, was still busy collecting materials from the old rocks, and building up the new. And so that age passed away like the former, and another came; and every age was represented by its own group of strata; and each group of strata was, in its turn, covered over with a new deposit; and the tombs were all sealed up, with their countless legions of dead, their massive monuments of stone, their strange hieroglyphic inscriptions. At length came the last stage of the world's history, and man appeared upon the scene" (pp. 23–25).

Here we have, in clear and distinct outline, at once the leading facts and the main theory of geology. Of the facts there can be no question. There are the rocks stratified and unstratified; open to the eye, open to the axe and the hammer. There are the stony skeletons and the stony footprints. These are the facts. That the earth's crust, as it now exists, came direct and at once from the hand of the Creator was the common belief before the dawn of modern inquiry. That, on the contrary, it was the result of many stupendous revolutions, the work of countless ages, carried on under the agency of fire and water; and that the skeletons and footprints now found imbedded in it are those of creatures that once lived and movedthis is the geological theory. To the elucidation of this theory, and of the arguments by which it is enforced and defended, Dr. Molloy devotes the remainder (nearly 300 pages) of the first section of his book. The following is his statement of the broad and general principle on which the whole fabric of the geological argument rests. It is given with the intrepid fairness and philosophic moderation which characterize the whole. discussion:

In the physical sciences it is a common principle of reasoning to account for the phenomena that come before us in nature by the operation of natural causes which we know to exist. Nay, this principle seems to be almost an instinct of our nature, which guides even the least philosophical amongst us in the common affairs of life. When we stand amidst the ruins of an ancient castle, we feel quite certain that we have before us, not alone the monument of time's destroying power, but also the monument of human skill and labour in days gone by. We entertain no doubt that ages ago the sound of the mason's hammer was heard upon these walls, now crowned with ivy; that these moss-grown stones were once hewn fresh in the quarry, and piled up one upon another by human hands; and that the building itself was designed by human skill, and intended for the purposes of human habitation and defence. Or, if we see a footprint in the sand, we conclude that a living foot has been there; and from the character of the traces it has left we judge what was the species of animal to which it belonged-whether man, or bird,

or beast. It is true that God is omnipotent. He might, if it had so pleased Him, have built the old castle at the creation of the world, and allowed it to crumble into ruins; or He might have built yesterday, and made a ruin begin to be where no castle had stood before, and covered the stones with moss, and mantled the walls in ivy. And as to the footprints in the sand, it were as easy for Him to make the impress there as to make the foot that left the impress. All this is true; but yet, if any one were to argue in this style against us, he would fail to shake our convictions: we should still unhesitatingly believe that human hands once built the castle, and that a living foot once trod the shore.

Now this principle of reasoning is the foundation on which the ablest modern geologists claim to build their science. The untiring hand of nature is ever busy around us; they ask us to come and look at her works, and to judge of what she has done in past ages by what she is now doing before our eyes. She is still, they say, building up her strata all over the globe, of limestone, and sandstone, and clay; she is still lifting up in one place the bed of the ocean, and in another submerging the dry land; she is still bursting open the crust of the earth by the action of internal fire, disturbing and tilting up the horizontal strata; she is still upheaving her mountains, and scooping out her valleys. All these operations are open to our inspection; we may go forth and study them for ourselves; we may examine the works that are wrought, and we may discover, too, the causes by which they are produced. And if it should appear that a very close analogy exists between these works that are now coming into existence, and the long series of works that are piled up in the crust of the earth, it is surely not unreasonable to refer the latter class of phenomena to the action of the same natural causes which we know to have produced the former (pp. 27-29).

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Having thus introduced our readers into the broad highway of the inquiry, our proper course, perhaps, should be to leave them to follow our author himself as he unfolds his "wild and wondrous" tale, and passes in review on his pictured canvas the marvels that are witnessed on the surface of the earth, or lie hidden in its depths and in the depths of the sea. But we would fain enrich our pages with a few selected details which, without over-testing the patience of those who are already acquainted with them, cannot but prove highly interesting to those who are not.

The process of denudation, which has from earliest time been going on over the whole surface of the earth, forms one of the broadest and most striking elements of the geological induction. It is so called from its denuding or laying bare surfaces that were previously covered. "The process of denudation is the work of many and various natural causes. Heat and cold, rain, hail and snow, chemical affinities, the atmosphere itself, all have a share in it; but the largest share belongs to the mechanical action of moving water. Every little rill that flows down the

mountain side is charged with finely-powdered sediment, which it is ever wearing away from the surface of its own bed " (pp. 21, 22). In the larger streams, the agency of denudation is of course still more conspicuous; but it is in the great rivers of the world that its mighty and extensive influence is seen. It has been calculated that the waters of the Rhine, impregnated as they are with carbonic acid, and therefore acting powerfully in dissolving limestone rock, carry each year to the sea a quantity of carbonate of lime sufficient for the formation of more than thirty thousand millions of oyster-shells. According to another calculation, founded on observations made with the greatest care, the river Ganges, during the four rainy months of each year, carries past a point, full five hundred miles distant from its mouth, the enormous quantity of six thousand millions of cubic feet of mud-a mass of mineral matter "sufficient to form a stratum of rock one foot in height, and two hundred and eighteen square miles in extent" (p. 37). Other high authorities tell us that the Mississippi sweeps down nearly four thousand millions of cubic feet of earth every year; while the Yellow River, in China, discharges not less than forty-eight millions every day.

So great are both the erosive and motive powers of current water, and so prodigious is the increase of this power in proportion to the increased velocity of the water, that we often read of common rivers, swollen by sudden rains, overflowing their banks, flooding the adjacent country, uprooting and crushing and sweeping before their mighty and merciless fury everything that impedes their course,-immense rocks, huge forest-trees, stately and strong-built houses, landmarks natural and artificial, which the hand of man or of time had been consolidating for generations. Thus, in the year 1829, "the river Dee swept away a bridge of five arches, built of solid granite, which had stood uninjured for twenty years; the whole mass of masonry sank into the bed of the stream and was seen no more (p. 42). So the river Don once heaved up an inclined plane, and left there, four or five hundred tons' weight of stone; and in the year 1827, an obscure rivulet in Northumberland swept to the distance of a quarter of a mile "a large block of greenstone-porphyry weighing nearly two tons" (ibid.). Examples of this kind might be multiplied without end.

These are, however, but limited and intermittent outbreaks of despotic power compared with the tremendous, ceaseless, world-wide assailing energies of the mighty Ocean-ẞalupperαo μεγα σθενος Ωκεανοιο. Round every island pillowed in the deep, round the great continents, against every rock-bound coast, through every inlet and fissure, day and night and day and

night for evermore, this mad war of water against land is raging, and its deafening and incessant roar is heard. Now tempestdriven, now tide-convulsed, now both together, with everunwearied force and in every clime, "the big waves lash the frighted shore." There is in the visible world no other conflict like this. Within the range of authentic history, islands that dotted the sea and braved its fury for ages, have been carried clean away, and left not a trace behind them. In the first half of the seventeenth century, an island, that about four centuries before had formed part of the mainland of Denmark, was flooded by the sea, and six thousand of the inhabitants perished: only three islet-fragments now remain, peering above the desolate waters; and they, too, are gradually melting away. The island of Heligoland, in the same sea, was, five centuries ago, four times as large as it is now: the little that still remains is becoming less and less; and it, too, in the course of time, will have vanished altogether. In many parts of the British Isles, the waste of land, by the inroads of the sea, has been going on in a similar way. Towards the close of the last century, a whole village on the eastern coast of Scotland was invaded by the sea, and in a single night swallowed up by the wild waves that are rolling there still. In England, the coast of Yorkshire is being to a great extent eaten away, and its tall chalk cliffs are crumbling into the whitened surf below. And so everywhere, age after age, this restless and potent creature carries on the work of Him who made it, and, for His own high designs, gave it that work to do.

So much for the denuding power of water in its fluid state. We should be glad to present our readers with some details of the power of the same element in its congealed form, especially of glaciers drifted out to sea, with huge masses of earth and stones imbedded in them or lying on their surface, and fastened thereto with icy cramps. These floating mountains, in this state called icebergs, are sometimes found to be several miles in length, rising above the water more than two hundred feet, and dipping into it more than a thousand feet. Approaching the warmer latitudes, they gradually melt into the sea, depositing at its bottom the stones and mud which they had torn from the denuded valleys thousands of miles away. But for the formation of these huge ice-hills, and for the effects they produce by land and sea; and for the constructing (we have spoken of the denuding) power of the watery element, which is being actually exercised over the globe, in the formation of stratified rocks, so closely resembling those that form the crust of the earth; and for the story of the fossil remains that are entombed in each successive tier of that crust; and for the geological argument

founded on these phenomena;-for all this we must send our readers to Dr. Molloy's book. Having thus dismissed the first great element, water, and the work it has been doing within the period of man's history, and the work it is thence so justly inferred to have done long before that history began, we have now to say a few words on the other great element-fire.

And here, as in the former case, there are the geological facts and the geological theory. That under the whole, or nearly the whole of the earth's crust, there lies a vast body of fire, is partly an attested fact, and partly an inference legitimately drawn from attested facts. From experiments and observations made in all parts of the earth, in coal-pits, mines, &c., it is found that, at no great distance below the surface, heat is felt very sensibly; and it is, moreover, found that the intensity of this heat increases rapidly in proportion to the depth. "In one and the same mine,' says Sir John Herschel, each particular depth has its own particular degree of heat, which never varies: but the lower always the hotter ; and that not by a trifling, but what may be called an astonishingly rapid rate of increase,-about a degree of the thermometer additional warmth for every ninety feet of additional depth, which is about 58° per mile!-so that, if we had a shaft sunk a mile deep, we should find in the rock a heat of 105°, which is much hotter than the hottest summer day ever experienced in England.' Now, if the temperature continue to increase at this rate towards the centre of the earth, it is quite certain that at no very great distance from the surface, the heat would be sufficiently intense to reduce the hardest granite and the most refractory metals to a state of igneous fusion" (p. 253).

There are other proofs of the existence of this subterranean fire, drawn from the volcanos, active and extinct, which are so widely scattered over the surface of the globe; and from hot springs, which are also found in almost every country in the world.

The Andes, the most remarkable of all mountain-ranges for its continuous length, extending from one extremity of South America to the other, "is studded over with volcanos, most of which have been seen in active operation within the last three hundred years" (p. 259). This vast volcanic chain, stretching along the Pacific Ocean, from Tierra del Fuego to the isthmus of Panama, rises again on the other side of that isthmus, and finally terminates only with the Rocky Mountains far on in North America. There are similar volcanic lines, though not extending so far, in Europe, Asia and Africa-to say nothing of the isolated groups of volcanos found in these continents or in islands of the ocean.

VOL. XIV.—NO. XXVIII. [New Series.]

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