BOOKS.
EARTH SCULPTURE.* HISTORY has a curious tendency to repeat itself in the realm of science-concepts as well as of politics. The earliest views of the earth regarded it as a personality, like ourselves, that lived, moved, breathed, grew old, and "quaked." Then came science and declared her to be merely an unchanging mass of lifeless solids, rolling impotently in a fixed, monotonous orbit. But the pendulum swung back, and less than fifty years ago Lyell and his followers began to assure us that if growth and change meant life, old Mother Earth not only had lived, but was still alive ; that the everlasting hills were mere wrinkles of age upon her cooling crust, and had been smoothed out in one place to reappear in another time and again in her history; that the celebrated remark of the Red Queen to Alice, "Call that a mountain I have seen mountains com- pared with which that is a valley," has its bizarre parallel • Sarth Sculpture. By James Gelkte, LL.D. London: J. Murray. [8a.] in the world of fact, in that several of our oldest mountain-chains are now represented by a-• low -line of hummocks like those in the LoWlands of. Scotland or the "Height of Land" across Eastern Canada, and in the ancient Appalachian chain the original lines of peaks are now represented by valleys, while the Alps, • the Andes, the Himalayas are mere creatures of yesterday com- pared with these. Not "every valley "has been " exalted," but every mountain and hill; that has lived long enough, has been "made low." Then came the physicists with their seismograph for registering the pulses of Demeter, and announced that not merely is.the solid earth beneath us an elastic film, like that of a thick soap-bubble, but that that film is in constant vibrations,-which so long as they are symmetrical We never notice, but which out of time we call "earth-quakes." And lastly, the round globe of our childhood has collapsed into- a hollow-faced "three-sided pyramid "—if we may be allowed the Ilibernicism—with the apex down. First it was of the shape of an orange, then of a peg-top, next—acme of filial insolence- " more like a potato," and finally science has frankly avowed its ignorance, and declares with Listing that the form of the earth is a geoid, which is, being interpreted, "earth- shaped." The North Polar Sea, with its wide belt of Siberian tundras in the Old World and caribou-barrens in the New, is the broad, hollow base of the "pyramid." The long ridge of the Rocky Mountains above and the Andes below is one of its projecting side-angles' the mountain backbone running from Scandinavia, through the Alps and Appennines vitt the central highlands of Africa to the Cape, is another ; and the Manchurian coign of granite stretching south - eastward through Siam, the Malay Peninsulas the volcanoes of the Archipelago; to Australia, is the third. And now upon this scientific scene of "no Heaven and a new earth-" comes Pro- fessor James Geikie in the latest of the admirable. "Pro- gressive Science Series," under the able editorship of Mr. F. E. Beddard, and proceeds to explain and graphically illustrate the changes which have taken place in the complexion and features of Mother Earth since her ribs and body-bulk were formed by the Titans below. Here the metamorphoses have been much more rapid and obvious. The present state of affairs is by no means a fair clear manuscript which he who runs may read, but a strange and complicated palimpsest in which the rude cuneiform of Archrean times shows dimly up through the rounded cursive of the Eocene. Land foram as we now see them depend upon three principal factors,—the shape of the original crust-foldings; the hardness of the rocks in the folds, and the force of the influences to which they have been subjected. These latter are of two classes,—the under- ground, heat and pressure, and the overground, water, air, and frost, or, as our author rather pedantically terms them hypogene, and epigene. These balance one another in a most curious manner' for while the giants of molten-rock oceans within are continually straggling up toward the surface even of highest mountain chains, and the relentless thrust of - the con- tracting crust is ever throwing up new mountain-wrinkles toward the very stars, epigene Nature, like Carlyle's democracy, is forever levelling downward. Ossa after Pelion, and Alp after Alp, have been melted down by the " secepe cadendo," which, as every schoolboy knows "eavat lapitlem," swept down into those hollows in earth's cheeks which we call oceans, there to cover the bottom in layer after layer, and by their weight upon the elastic crust cause other mountains to bulge upward on the land they have left. Many of our plains to-day are simply the broad bases of huge mountain ranges.
Professor Geiltie accordingly divides mountains Into two great classes, tectonic or "original," the remains of the great crust-folds just as they were thrust up, among which are all our modern, geologically speaking, "seventeenth-century" mountains, the Alps, the Himalayas, and the Cordilleras; and relict mountains, which, as their name implies are the "rem- nants" or hardest rock masses of older folds which alone have resisted the elements, while all the softer strata in which they were imbedded, or even underwhichtheywere originallyburied, thousands of feet, have been crumbled down and washed away. Such are the red sandstone hills 'of. Sutherland, the hills of Saxon Switzerland, and the buttes and mesas of Colorado and Arizona. In this sort of struggle " survival " depends not only upon hardness, but also upon arrangement of strata. Just as in the Wave the crest breaks while the trough does not, so in our land-billows the strata on the crests of the folds are nearly always fractured, and hence let in the water, and break down much more rapidly than the more gently bent and unbroken portions in the troughs between them. So that with the pro- cess of eons we get the curious, and even anomalous, condition already alluded to in the Alleghany Mountains, where the crests or anticlines have worn away not only to the level of, but far below, the original valley-troughs or synclines, so that the latter now are found at the tops of the present mountain ranges, while the erstwhile chains of peaks have been literally eroded into valleys.
In short, if your mountains be recent, which is fortunately the case with nearly all popularly included under that title, all that are considered worthy of the notice of the Alpine Club, for instance, then the peaks and ranges will be anticlinal, and the valleys mostly synclinal ; if, on the other hand, they are really ancient and low in proportion, then just the reverse is very apt to be the case. So that "old as the hills," not mountains, is a singularly apt and felicitous metaphor.
And this method of classification is extended to, and in part explains, the other chief features of the landscape. Valleys are similarly divided into original and subsequent, but here the latter are by far the more common. A few streams still run: in the troughs of the original crust-waves, but when Nature with her rain-blest and her ice-plough is ruthlessly planing down the mountain-folds to their very bases, the water- flow quickly finds out the softest bed to run in, and follows the line of those strata which are most easily channelled out ; and these, as we have seen, are more apt to be those of the anticlines than of the synclines. As our author graphically says, "they are simply hollows which have been worked out along lines of weakness." And oddly enough, negative as mere hollows essentially are, they are far more persistent and permanent than their complements, mountains. Once a stream of any size has fairly carved out its valley, it is almost impossible to obliterate it save by the upheaval of another crustal fold directly across its course. And even this will not always destroy it, for the rate of upheaval being slow, the stream will steadily saw its way down through the fold as fast as it rises under its bed, and wear for itself a rocky gorge thousands of feet deep by the time the elevation is completed, as the celebrated Colorado River has done within very recent geologic times. Flowing resistlessly in their never-ceasing, earth-to-cloud circuit, the waters make the lakes "the burial places of their surrounding mountains," and the oceans the grave of the continents. The dry land is continually melting down and flowing into the sea, or, in the words of our author, a constant "flattening out of the land- scape with extension" is going on. It is something of a surprise to most of us, who have been accustomed to regard a monotonous level as the common or normal condition of land-surfaces, to learn that most plains have been literally " planed " down to their present level, and, like certain poets, are made, not born. Land is thrown up literally "in the rough," and plains are made either by the burying of the lowest areas, under layers of sediment from the waters of lakes, seas, or rivers, which accumulate there, plains of accumulation, or by rasping all projections down by rain or glaciers to a broad base-level, plains of erosion.
The steppes of Russia, the tundras of Siberia, and the prairies and pampas of America are instances of the former type, and the coal-regions of Belgium and Northern France, the Low- lands of Scotland, and the great central plateau of Africa of plains of erosion.
The subject-matter of the book is interesting and well written, but its arrangement leaves much to be desired. It is marred by both repetitions and obscurities, for lack of a good introductory chapter dealing with the principles involved and explaining the new, and in some cases original, terms used. This is partly compensated for by a glossary, but we should certainly advise the general reader to begin with the last chapter but one, as a'clue to the sometimes involved descrip- tions of the body of the book. The paper and presswork are unusually good, but the lettering of the numerous illustrative "sections" is, we regret to say, in a small and crabbed cursive most trying to the eyes, and in places illegible.
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