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 ALPS

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as inseparable from the Apennines on the one side and the mountains of Istria and Dalmatia on the other, and as related in some way or other to the basin of the Adriatic and the plain of Northern Italy. But putting aside this more general question and restricting ourselves to the Alps proper, we must bear in mind two facts in any attempt to explain their complications :—(1) This chain was not the product of a single set of movements, but of two at least, which were separated by a considerable interval: the one occurring when the Eocene was passing into the Oligocene, the other in like way between the Miocene and Pliocene. (2) That the sedimentary masses thus affected were deposited on an irregular floor of more ancient, chiefly crystalline, rocks; parts at least of the present site of the Alps having been mountainous districts in Carboniferous and again in Permo-Triassic times. These irregularities in the thickness and strength of materials would cause corresponding inequalities in their resistance to pressure, and thus introduce numerous comportion. But on examination irregularities appear which plications. Still, though allowance must be made for are far from unimportant. The southern sedimentary zone, them, the general process in the rise of the Alps for instance, gradually becomes attenuated as it is followed can be inferred from the experiments of A. Favre, from its eastern end westwards, till it disappears rather H. M. Cadell, and Bayly Willis, and be described as beyond Lago Maggiore, after which crystalline rocks follows :—Lateral pressures have formed a group of great rise directly from the Piedmontese plain. The structure folds in the earth’s crust; these sometimes have been of the chain, also, is the most simple in its eastern part, gradually bent over until their axial planes became a central range of crystalline rock forming the watershed, inclined to the horizon. The strain occasionally has with two masses of sedimentary rocks flanking it north continued till the masses have been ruptured along these and south, through which the rivers have cut their paths. planes, and the upper portion of the fold has then slid on But this structure, as we approach the headwaters of above the lower, thus producing an “overthrust fault.” the Inn, becomes more complex, as we shall explain in During these processes the less pliant crystalline masses speaking of the hydrography, the change being probably are crushed and sheared, thus giving rise to structures connected with a feature in the geology. The outcrops of analogous to cleavage, and often suggestive of bedding. the rocks, as we have said, conform to the general course The remarkable folding in the Alpine rocks has long been of the chain at its eastern end, trending almost west, but known, but the recognition of these other structures is then they gradually sweep round the north Italian plain till comparatively recent, and its absence seriously detracts at last they are almost parallel to their original direction. from the value of not a few geological maps and memoirs. This structure, however, is modified by another of minor, One instance may suffice as an example :—The North but sometimes considerable importance, which is most Swiss Alps between the valleys of the Beuss and the conspicuously exhibited in the district about Lago di Bhine, especially near the Glarnisch, exhibit a singularly Garda. Here a broad belt of Mesozoic sedimentary rock, complicated structure, the strata apparently being bent bounded on the south by a line extending approximately over to form a double fold, with complete inversion on from Brescia to Verona, runs across the chain in a both sides. No doubt the arrangement of the strata N.N.E. direction; flanked on the west by crystallines, suggests this structure ; but the mechanics of the process and on the east, though less continuously, by the same are so difficult to understand that Bothpletz with several and by great masses of Permian “porphyry.” This belt other authorities explains it as a combination of overfoldmay be traced by outlying patches across the central range ing followed by great overthrust faulting, and this seems until near Innsbruck it apparently dies out against the to the present writer far more probable. Another perplexing structure may be mentioned here northern sedimentary range. It is in this neighbourhood, and the coincidence is significant, that the Alps attain their which is found in certain mountains on the northern face greatest width from north to south. Here, in fact,, the of the Alps, such as the Mythen and Stanzerhorn, and has dominant wave-like folds, of which the Alpine chain is of late attracted much attention. These, called Klippen, composed, are traversed obliquely by a syncline. To the are abrupt pyramidal masses, the beds in the upper part west of this, passing approximately between Chur and being not only older than those in the lower, but also Mals, we find traces of a second syncline with the same “ contorted, fractured, crushed, and mixed up,” while the general trend, but possibly subdivided by a central rise, newer are comparatively undisturbed. They are due to while the structure of the crystalline rocks between the overfolding and overthrusting, being remnants of larger two main synclines hints at the existence of a corre- masses, the greater part of which has been removed by sponding anticline. A similar structure is suggested in denudation; but that they have been forced into their the Bernina group, and yet farther to the west (in maps present position from so great a distance as the Brian§onon a larger scale); while from Mont Blanc for a con- nais, as some have suggested, is hardly possible. It is now generally admitted that the valleys in mounsiderable distance to the south the whole chain has a general trend, in the same direction, and that is repeated tain regions are mainly the results of denudation, though uy(jroby the outlying crystalline masses, the outcrops of which, the movements and structures of the uprising grapby. as far as Dauphine, run conspicuously from N.N.E. land masses must have done much, especially at to S.S.W. How this structure is connected with the first, to determine the directions in which the making of the Alps will be presently considered. But since water ran. Thus the Alpine valleys may be divided ridge and furrow, swelling and dimple, are closely related broadly into valleys of dip and valleys of strike—the former, on the earth’s surface, any complete discussion of the as the name implies, following the dip of the strata, physical history of the Alpine chain must regard it and so being the narrower and steeper; the latter running

not known to occur elsewhere in the Alps ; in other places, for example near Sepey, the erratics may not have come from any great distance. But it is difficult to account for their presence. Ice is the most obvious means of transport • but the temperature during Eocene and Oligocene ages appears to have been much higher than it now is, being at a maximum in the former, while no evidence can be found of the existence of mountains on or near the present site of the Alps. Some authorities place the requisite range immediately to the north, supposing its roots to be buried beneath the Miocene deposits of the Swiss lowlands, but it would be strange if such an important mass had so quickly vanished and left “ not a rack behind.” A geological map of the whole Alps, on a scale large •enough to indicate clearly the above-mentioned divisions, shows them to be arranged in zones which are Geological ruqe}y symmetrical with the outline of the structure. the crystalline rocks occupying its central