48 Professor Bronn on some Geological and Physical 



exactness the strata with which the one series begins and the 

 other ends, as these beds pass into one another gradually and 

 in a conformable position. 



V. Up to the present time the rocks of the trii^s and those 

 of the coal or transition series seemed to be the most dis- 

 tinctly separated ; a wide gap appeared to be opened up be- 

 tween them. This blank, however, has also very lately been 

 filled up, since the appearance of the work by Munster and 

 Wissmann on St Cassian. The formation of St Cassian, for 

 so long a period a puzzle, has ended by becoming the explana- 

 tion of another puzzle, the separation between the coal forma- 

 tion and the trias. It is a previously unknown link between the 

 two periods, which, out of 422 species, contains 386 locally pe- 

 culiar to it, and, among the 36 remaining species, has 22, which 

 are one-half common with the transition rocks and the other 

 with the trias ; in favour of which double connection, the genera 

 distinguished as belonging to the two give just as strong in- 

 dications as the species. When, then, besides these there are 

 some species partly analogous to, and partly identical with, 

 those of more remote formations, viz. 11 with the Has, and 

 3 with the Jura, this scarcely amounts to a larger quota 

 than occurs in other formations, but which I shall not enume- 

 rate, in order that I may not be too prolix. I would merely 

 refer to the Lethda, to Hisinger, Von Buch (on Terebratulas), 

 Adolphe Brongniart, D'Archiac, De Verneuil, &c. 



Thus, then, the results of recent investigations havij con- 

 firmed and justified what I asserted in 1832, that such cases 

 must, in the mean while, be considered apart and isolated 

 from the others, until more minute researches on the very 

 spot should either teach us something different, or shew the 

 cause of the mixture of fossils from different formations. If, 

 however, we must admit such a mixture for the products of 

 different periods, how much more will it be the case for the 

 products of different formations or groups of formations of 

 one period ! When I read, three or four years ago, the asser- 

 tion of Murchison and De Verneuil (which, however, was after- 

 wards much limited by themselves), that all the fossil species 

 of the Cambmn, the Silurian, the Devonian, and the moun- 



