BARRANDE ON THE TRILOBITES OF BOHEMIA. 39 



— The passage from the lower beds to these is conformable, and 

 the transition perfect. The beds of this group are more argillaceous 

 than those of the former; and they may even be regarded as nodules 

 of limestone in a fine argillaceous base. The limestone is fine and 

 compact ; its colour grey, reddish, and blackish. The bands of 

 limestone are sometimes separated by schists finely laminated. 



The central palaeozoic basin of Bohemia terminates with these 

 calcareous beds, which are here and there covered up by the Quader- 

 sandstein. The thickness of the beds on the whole amounts to about 

 200 feet. 



2. Palceontological characters. — It would appear that the condi- 

 tions of the palaeozoic seas were gradually becoming less and less 

 favourable for the existence of organic beings. All the moUusca 

 have disappeared almost at once in these beds, or are reduced to a 

 small number of species and individuals, and in many cases the cal- 

 careous portion of the shells has been removed. The fossils are 

 thus very diflficult to determine. 



The Trilobites form the only exception to this condition : owing 

 to the nature of their covering, they have been usually sufficiently 

 well preserved to furnish the means of determination. 



Both in variety of species and number of individuals, the Trilobites 

 in these deposits had become predominant ; and the author describes 

 sixteen species, four of which also occur in the next lower group. 

 There is little means of comparison between these beds and those 

 of other countries. 



The author then concludes with the following resume oi the most 

 remarkable facts suggested in his memoir. 



1. The palaeozoic basin of the centre of Bohemia considered as a 

 whole is extremely rich in Trilobites, most of them unknown. These 

 are abundant in the lowest fossiliferous beds, less prominent in the 

 middle, but again dominant in the newest deposits of the basin. 



Since Trilobites specially characterise Silurian formations, all the 

 formations in this Bohemian basin are exclusively of that period. 

 This is recognized at once by an examination of the fossils in spite 

 of the Devonian look of some of them at first sight. 



2. Excluding the two groups A, B, which form the base of the 

 system, and which have been called Azoic, the other groups (C, D, 

 E, F, G,) offer well-marked palteontological characters correspond- 

 ing to as many local creations each different and successive. These 

 characters are based partly on the almost total difference between the 

 Trilobites of each group, and partly on the predominance of certain 

 mollusca in some groups and the almost total absence of identical 

 species of these animals as well as Trilobites in adjacent groups. 



3. The two lower fossiliferous groups C, D, form a division entirely 

 distinct, geologically, and above all palaeontologically, from the three 

 upper groups E, F, G. 



4. There are thus three great natural divisions in the succession 

 of formations in this Bohemian basin, the lower division being azoic, 

 and the middle and upper divisions fossiliferous. 



These correspond exactly with those recognized in Great Britain 

 under the names of . . 



