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Show I·· i!i I' il I :I ~~ l I ~ ~ 1, \ rt· ! ' }.. ·'· l \ I I I \ I ~ I l ,•' I I \ ~ ;' • :l ~ I I J ! 'j ,·II iLh ! ~ i I I .d '. I ! I i',ol 1 I i'j: 1 1·1' til :,.11·:: ... j•: i )i ~~~ ,J, I" . ·- 1\ i ' ~ :_1 • "· 210 MIOCENE PERIOD. [Ch.XV. a sea-cliff, when the whole country stood at a lower level No. 53. L~--------c----------~0~·~<~~~-~~ 8 ection of Inland cliff at Abesse, nem· Da:t. a, Sand of the Landes. b, Limestone. c, Clay. relatively to the sea. But this can no lon?er be regarded as matter of conjecture. In makiug excavatiOns ~·ecently for the foundation of a building at Abesse, a quantity of loose sand, which formed the slope d, e, was removed, and a perpendicular cliff exposed about 50 feet in height. The bottom of this cliff consists of limestone, b, which contains shells and corals of Miocene species, and is probably a calcareous form ~f the division c (diagram No. 51, p. 207). Immediately below this limestone is the clay c (probably d, diagram No. 51, p. 207), and above it the usual tertiary sand a of the department of the Landes. At the base of the precipice are seen large, partially-rounded, masses of rock, evidently detached from the stratum b. The face of the limestone is hollowed out and weathered into such forms as are seen in the calcareous cliffs of the adjoining coast, especially at Biaritz, near Bayonne*. It is evident that, when the country was at a somewhat lower level, the sea advanced along the surface of the ·argillaceous stratum c, which, by its yielding nature, favoured the waste and undermining of the more solid superincumbent limestone b. Afterwards, when the country had been elevated, part of the sand a fell down, or was drifted by the winds, so as to form the talus d, e, which masked the inland cliff until it was artificially laid open to view. The situation of this cliff is interesting, as marking one of the p~u ses which intervened between the successive ~ovements of elevation whereby the marine tertiary strata of this country "' This spot was pointed out to me by the Froprietor of the lands of Abesse in 1830. Ch. XV.] MONT FERRAT AND THE SUPERGA. 211 were upheaved to their present height, a pause which allowed time for the sea to advance and strip off the upper beds a, b, from the denuded clay c. Hills of Mont Ferrat and the Superga.-The late Signor Bonelli of Turin was the first who remarked that the tertiary shells found in the green sand and marl of the Superga near Turin differed, as a group, from those generally characteristic of the Subapennine beds. The same naturalist had also observed, that many of the species peculiar to the Superga were identical with those occurring near Bordeaux and Dax. The strata of which the hill of the Superga is composed, are inclined at an angle of more than 70 degrees. ".rhey consist partly of fine sand and marl, and partly of a conglomerate composed of priII'! ary boulders, which forms a lower part of the series, and not, as represented by M. Brongniart by mistake*, an unconformable and overlying mass t. This same series of beds is more largely developed in the chain of Mont Ferrat, especially in the basin of the Bormida. The high road which leads from Savona to Alessandria intersects them in its northern descent, and the formation may be well studied along this line at Carcare, Cairo, and Spinto, at all which localities fossil shells occur in a bright green sand. At Pian'a, a conglomerate, interstratified with this green sand, contains rounded blocks of serpentine and chlorite schist, larger than those near the summit of the Superga, some of the blocks being not Jess than nine feet in diameter. When we descend to Aqui, we find the green sand giving place to bluish marls, which also skirt the plains of the Tanaro at lower levels. These newer marls are associated with sand, and are nearly horizontal, and appear to belong to the o]der Pliocene Subapennine strata t· The shells which characterize the latter, abound in various parts of the country near Turin; but that region has not yet been examined with sufficient care to enable us to give exact sections to illustrate the superpo· "' Terrains du Vicentin, p. 26. t I examined the Superga in company with Mr. Murchison in 1828, t See section, wood-cut No, 4, p. 21. :; ' I . '1 : I l 1 |