M. Barrande on (he Silurian System of Bohemia. 119 



The upper stage, or the Culminating slates, H, appears 

 only in a few isolated patches, sometimes, however, 100 

 metres thick, and was at first conjoined with the former 

 group. It consists chiefly of grey or yellow slates of little 

 consistence and mixed with a few beds of impure quartzite. 

 In one place near Hostin, a thin layer of coal, 3 to 4 centi- 

 metres (1 to 1^- inch) thick, is seen among the slates. Here 

 and there a few impressions of Fucoids or other plants, but 

 very indistinct, occur, and are the only trace of vegetable life 

 in the whole of this upper division. The fauna is extremely 

 poor compared to the former groups, being comprised in a 

 few species. The Trilobites have furnished one Phacops and 

 one Proetus ; the Cephalopods, two Orthoceratites and a Lit- 

 uite ; the Gasteropods some indistinct casts. The Brachiopods 

 are represented by a Leptcena and a Terebratula ; the Ace- 

 phalse by an Avicula. The Tentaculites are, however, pretty 

 abundant in these localities. This paucity in the fauna may 

 mark merely the continued decrease of life already noticed, 

 or may depend on the want of calcareous matter in the rocks. 



In comparing this higher division of the Bohemian Silurians 

 with the formations of other countries, the author proceeds 

 on the principles, that in these ancient seas, as in those of 

 the existing world, some species were pretty generally dis- 

 tributed, though certain isolated basins might have a fauna 

 in great part peculiar. A new species diffused from a point 

 may also have appeared at different times in distant locali- 

 ties, and hence the occurrence of its remains in two isolated 

 deposits is no proof of exact contemporaneity. Where many 

 identical species occur, they, however, shew that the forma- 

 tions were not more widely separated than by the mean 

 duration of a species, and were thus relatively contempo- 

 raneous. With these explanations, Bohemia shews many 

 points of analogy with other Silurian countries. These rela- 

 tions do not depend on geographical proximity, for the depo- 

 sits of Franconia have less analogy to those of Bohemia than 

 those of England and Sweden, and scarcely so much as those 

 of North America. Again, these relations vary from age to 

 age. Thus the protozoic group C, with the same or corre- 

 sponding generic types, has yet no common species with 



