Ch. XV.] 



CRAG AND FALUNS COMPARED. 205 



fresh-water shells, together with sand and pebbles, and occa- 

 sionally, perhaps, sweep down the carcasses of land quadrupeds 

 into the sea. If the sand and shells, both of the 'crag 5 and 

 the ' 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 con- 

 tents, 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 we 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 Mediterranean 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 greatly on the 

 increase in European latitudes during the more modern geolo- 

 gical eras. 



In the faluns, and in certain groups of the same age, which 

 occur not far to the west of Orleans, M. Desnoyers has dis- 

 covered the following mammiferous quadrupeds. Palceothe- 

 * See above, chap. x. 



