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Show 166 OLDER PLIOCENE PERIOD. [Ch. XII, Genoa.-At Genoa the tertiary strata consist of blue marls like those of the northern Subapennines, and contah~ the same shells. On the immediate site of the town they rise to the height of only 20 feet above the sea, but they reach about 80 feet in some parts of the suburbs: At the base of a mountain not far from the suburbs there is an ancient Monte d'Origiua. No. 28. Position of Tertiary strata at Genoa. a, Ancient sea-beach. b, Blue marl with shells. C, Inclined secondary strata of sandstone, shale, &c. beach, strewed with rounded blocks of Alpine rocks, some of which are drilled by the 1'rfodiola lithophaga, Lamk., the whole cemented into a conglomerate*, which marks the ancient sea-beach at the height of 100 feet above the present sea. Savona.-At Savona, proceeding westwards, we find deposits of blue marl like those of Genoa, and occupying a corresponding geological position at the base of the mountains near the sea. The shells, collected from these marls by Mr. Murchison and myself, in 1828, were examined by Signor Bonelli, of Turin, and found to agree with Subapennine fossils. Albenga.-At Albenga these formations occupy a more extensive tract, forming the plains around that town and the low hills of the neighbourhood, which reach in some spots an elevation of 300 feet. The encircling mountains recalled to my mind those which bound the plain and bay of Palermo, and - * I have to acknowledge the assistance of Professor Viviani and Dr. Sasso who called my attention to these phenomena when I visited Genoa in Jan. 1829. Ch. XII.] TERTIARY STRATA AT NICE. 167 other bays of the Mediterl'anean, which arc surrounded by bold rocky coasts. 'rhe general resemblance of the Albenga strata to the Subapennine beds is very striking, the lowest division consisting of blue marl, which is covered by sand and yellow clay, and the highest by a mass of stratified shingle, sometimes consolidated into a conglomerate. Dr. Sasso has collected about 200 species of shells from these beds, and it appears, by his catalogue, that they agree, for the most part, with the northern Subapennine fossils, more than half of them belonging to recent species*. Nice.-At Nice the tertiary strata are upraised to a much greater height, but they may still be said to lie at the base of the Alps which tower above them. Here, also, they consist principally of blue marl and yellow sand, which appear to have been deposited in submarine valleys previously existing in the inclined secondary strata. In one district, a few miles to the west of Nice, the tertiary beds are almost exclusively composed of conglomerate, from the point of their junction with the secondary strata to the sea. The river ~agnan :flows in a deep valley which terminates at its upper extremity in a narrow ravine. Nearly vertical Monte Calvo. No. 29. Section from ltfonte Calvo to tile sea hy tl1e valley of Magnan, near Nice. A, Dolomite and sandstone. (Green-sand formation?) a, b, d, Beds of gravel and sand. c, Fine marl and sand of St. Madeleine. * Giornale I~igustico, Genoa, 1827. |