CXVIU PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



local difference between the fauna of these marls and that of either 

 the north-east of Switzerland, or of the molasse of Mount Moliere, 

 associated geologically with them ; this latter deposit having yielded 

 the remains of at least four species, not absolutely determinable, 

 though distinguishable from any of the preceding. The E?ni/s Lakarpi, 

 Pict. and Humb., and the Emi/s Charpentieri, Pict. and Humb., were 

 found only in the lignites of Lausanne ; the Emys Gaudini, Pict. 

 and Humb., the Cistudo Razoumowskyi,Y\ei. and Humb., MidCistudo 

 Morloti, Pictet and Humb., in the molasse of Lausanne ; whilst 

 the fragments found in the contemporaneous molasse of Vengeron, 

 though not sufficiently perfect to be accurately determined, are yet 

 sufficiently so not to be confounded with the preceding species. 



In addition to the land- and marsh-tortoises of the preceding de- 

 posits, various remains of fluviatile Chelonians have been found, 

 which M. Pictet refers to at least three distinct species ; namely, 

 1st, a true Trachyaspis, fragments of which have been found in the 

 molasse of the Canton de Vaud and in the molasse of Mount Mo- 

 liere, so that these fragments, belonging to the same species, that is, 

 the Tr. Lardy i, H. von Meyer, form an organic link between the two 

 deposits ; 2nd, a species of Trionyx in the molasse of Yverdun ; and 

 3rd, a species of either Trionyx or Trachyaspis in the lignites of 

 Rochette. The deposits of CEningen have yielded no new species, 

 but possess their own representatives in the Chelydra Murchisoniy 

 Bell, and the Emys scutella, H. von Meyer. 



What a curious picture of the former condition of Switzerland 

 does this local distribution of the Chelonians afford, and how dif- 

 ficult to explain it, unless indeed the sluggish nature of these animals 

 may be deemed sufficient to account for the limitation of their range 

 of existence ! MM. Pictet and Humbert appear to have taken great 

 pains in comparing their species with those described by preceding 

 writers, and, though the differences in some instances are small, it is 

 probable that the species are really well-established. The Chelo- 

 nians, however, of some tertiary deposits have not yet been described, 

 and the authors therefore have been unable to bring the Swiss deposits 

 into comparison with them ; it can scarcely, however, be expected 

 that species so locally restricted in Switzerland should be found to 

 have a more general and enlarged range elsewhere. 



I have dwelt thus long on these writers, in order to illustrate 

 the necessity, in the present state of geology, of first co-ordinating 

 together those members of the tertiary formations which appear to 

 have had a geographical connexion between them, before attempting 

 to extend that co-ordination to distant and strongly separated lo- 

 calities. The Mediterranean has now a fauna marked by many 

 peculiarities, and its tertiary deposits were characterized by similar 

 peculiarities; and, in effecting the more general correlation, it is there- 

 fore necessary to advance step by step in establishing the correlation 

 of adjacent deposits before attempting that of the more distant. 



Mr. Prestwich has pointed out the peculiarities of the Paris basin, 

 as distinguished from those of the London basin, and suggested that 

 the true mode of comparing two such parallel deposits, is by observing 



