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Show 164 OLDER PLIOCENE PERIOD· [Ch. XII. . . 1 · t 1 kes such as that of the causes wluch dnfted ske etons m o a ' . V l d upper a 'Ar no, may have c'a rried down others mto. .fi rths or f I 'l'l femur of an elephant has been d1smterred bays o t 1e sea. 1e . . wi· t I tt hed to it showing that 1t remamed for some 1 oysters a ac ' . . time exposed after it was dnfted mto the sea. Strata at the base of the Maritime Alps.-If we pass from the Italian peninsula, and, following the borders of the Medi-terranean, examine the tertiary strata at . the . foot of .t he Maritime Alps, we find formations agreemg m ~oologiCal characters with the Subapennine beds, and pr~sentmg many points of analogy in their minera~ composition. The Alps, it is well known, terminate abruptly m the sea, between Genoa and Nice, and the steep declivities of that bold coast are continuous below the waters, so that a depth of many hundred fathoms is often found within stone's-throw of the beach. Exceptions occur only where streams and torrents enter the sea, and at these points there is always a low level tra~t~ intervening between the mouth of the stream and the prec1p1tous escarp-ment of the mountains. In travelling from France to Genoa, by the new coast-road, we are principally conveyed along a ledge excavated out of the side of a steep slope or precipice, in the same manner as on the roads which traverse the great interior passes of the Alps, such as the Simplon and Mont Cenis, the difference being that, in this case, the traveller has always the sea below him, instead of a river. But we are obliged occasionally to descend by a zig-zag course into those low plains before alluded to, which when viewed from above, have the appearance of bays desert~d by the sea. They are surrounded on three sides by rocky eminences, and the fourth is open to the sea. These leading features in the physical geography of the country are intimately connected with its geological structure. The rocks composing the Alpine declivities consist partly. of primary formations, but more generally of secondary, wh~ch have undergone immense disturbance; but when we examme the low tracts before-mentioned, we find the surface covered Ch. XII.J STRATA AT TilE BASE Qlr THE MARITIME ALPS. 165 with great beds of gravel and sand, such as are now annually brought down by torrents and streams in the winter, and which are spread in such quantity over the wide and shifting riverchannels as to render the roads for a season impassable. The first idea which naturally suggests itself, on viewing these plains, is to imagine them to be deltas or spaces converted into land by the accumulated sand and gravel brought down from the Alps by rivers. But, on closer inspection, we find that the apparent lowness of the pla.ins, which at first glance might be supposed to be only just raised above the level of the sea, is a deception produced by contrast. 'l'he Alps rise suddenly to the height of several thousand feet with a bold and precipitous outline, while the country below is composed of horizontal strata, which have either a flat or gently-undulating surface. These strata consist of gravel, sand, and marl, filled with marine shelJs. They are considerably elevated, attaining sometimes the height of 200 feet, or even more, above the level of the sea; there must, therefore, have been a rise of the coast since they were deposited, and they are not mere deltas or spaces reclaimed from the sea by rivers. Why, then, are the strata found only at the points where rivers enter? We must imagine that, after the coast had nearly acquired its present configuration, the streams which flowed down into the Mediterranean produced shoals opposite their mouths by the continual drifting in of gravel, sand, and mud. 'I'he Alps were afterwards raised to a sufficient height to cause these shoals to become land, while no perceptible alteration was produced on intervening parts of the coast, where the sea was of great depth near the shore. The disturbing force appears to have acted very irregularly, and to have produced the least elevation towards the eastern extremity of the Maritime Alps, and a greater amount as we proceed westward. Thus we find the marine tertiary strata attaining the height of about 100 feet at Genoa, 200 and 300 feet farther westward, at AlbenO'a, and 800 or 900 feet in the . 0 n~1ghbourhood of Nice, |