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Show 204 MIOCEN g PERIOD. [Ch, XV. terrestrial quadrupeds belong to the genera Masto~on, Rhino. ceros, H1. ppopo tamus, &c ., the assemblage, co.n sidered as a w1 1 01 e , b e·m g vet· y distinct from those of the Parn 's gyp• sum. I examined several detached patches of the 1 ourmne beds, where they rest on primary strata in the env~rons o.f Nantes, particularly one locality at Les Cleans, about eight miles southeast of that town, and was struck with the evidence afforded by them of the emergence of large intervening tracts of granitic schist since the Miocene era, which we might otherwise have su posed to have been raised at a very remote epoch. It is propb able that these patches of tert1. ary d epos1. ts were . . I ongm~ ly local, having been thrown down wherever the set of the t1des and currents permitted an accumulation to take place. The faluns and contemporary strata of the basin of the Loire may be considered generally as having been formed in a shallow sea, into which a river, flowing perhaps from some of the lands now drained by the Loire, introduced from time to time flu. viatile shells, wood, and the bones of quadrupeds, which may have been washed down during floods. Some of these bones have precisely the same black colour as those found in the peaty shell-marl of Scotland ; and we might imagine them to have been dyed black in Miocene peat which was swept down into the sea during the waste of cliffs, did we not find the remains of cetacea in the same strata, bones, for example, of the lamantine, morse, sea·calf, and dolphin, having precisely the same colour. Comparison of the Faluns of the Loire and the English Orag.-The resemblance which M. Desnoyers has pointed out as existing between the English C'rag and the French faluns is one which ought by no means to induce us to ascribe a contemporaneous origin to these two groups, but mer~ly a si.miJarity of geographical circumstances at the respective ~erwds when each was deposited. In every age, where there 1~ land and sea, there must be shores, shallow estuarie.s, and nvers; and near the sea-coasts banks of marine shells and c~rals .m~y accumulate. It must also be expected that rivers wtll dr1ft ln Ch. XV.] CRAG AND PALUNS COMPARED. 205 fresh-water shells, together with sand and pebbles, and occasionally, perhaps, sweep down the carcasses of land quadrupeds into the sea. If the sand and shells, both of the 'crag' and the r faluns' have each acquired the same ferruginous colour, such a coincidence would merely lead us to infer that, at each period, there happened to be springs charged with iron, which flowed into some part of the sea or basin of the river, by which the sediment was carried down into the sea. Even had the French and English strata which we are comparing shared a greater number of mineral characters in common, that identity could not have justified us in inferring the synchronous date of the two groups, where the discordance of fossil remains is so marked. The argument which infers a contemporaneous origin from correspondence of mineral contents, proceeds on the supposition that the materials were either washed down from a common source, or from different sources into a common receptacle. If, according to the latter hypothesis, the crag and the faluns were thrown down in one continuous sea, the testacea could not have been so distinct in two very contiguous regions, unless w~ assume that the laws which regulated the geographical distribution of species were then distinct from those now prevailing. But if it be said that the two basins may have been separated from each other, as are those of the 1\fediterranean and Red Sea, by an isthmus, and that distinct assemblages of species may have flourished in each, as in the example above-mentioned is actually the case*, we may reply that such narrow lines of demarcation are extremely rare now, and must have been infinitely more so in remoter tertiary epochs, because there can be no doubt that the proportion of land to sea has been g1·eatly on the increase in European latitudes during the more modern geological eras. In the fuluns, and in certain groups of the same age, which occur not far to the west of Orleans, M. Desnoyers has discovet ·ed the following mammiferous quadrupeds. Palceothe- • Sec above, cha11, x. |