238 PROCEEDINGS OP THE AMERICAN ACADEMY 



species ; and hardly any genera exist between the primordial groups 

 and tliose of the second fauna. In a word, the record of the palseon- 

 tologic register of Bohemia is incomplete. It is evident that, although 

 the development of life was interrupted in Bohemia, it must have con- 

 tinued elsewhere ; for, once begun, nothing short of the destruction of 

 the earth could stop the evolution of living forms. Thus, a fauna was 

 shortly found not far from Bohemia, composed of the true primordial 

 types, with a mixture of forms whose extended developmeut was only 

 reached during the existence of the second fauna. Dr. Gurabcl, director 

 of the geological survey at Ilof, in Bavaria, in 1862 found this inter- 

 mediate fauna. Studied by Barrande in 18G3, this savant recognized 

 that, beside the primordial types, such as Olenus and Conocephalites, 

 there are forms of the second fauna of Bohemia, as Asaphus, CaJy- 

 mene, and Cheirurus, but belonging to different species. Then, sup- 

 porting himself on the absence of the Paradoxides type at Hot, he 

 concludes " that the fauna of Ilof is posterior to the primordial fauna 

 of Bohemia." And he adds : '' Thus the fauna of Ilof appears to cor- 

 respond to an intermediary epoch between our primordial fauna and 

 that of the first phase of our second fauna. This intermediary age is 

 not represented by any fauna in our basin [Bohemia]. But it is 

 natural to conceive that it corresponds to the time during which the 

 masses of porphyry overflowed into the Silurian sea of Bohemia, which 

 are intercalated between the strata enclosing our first two faunae. In 

 effect, the plutonic phenomena which introduced these rocks into our 

 formations must have made the sea of these regions uninhabitable to 

 the contemporary faunae." * However, the deposit at Ilof is isolated, 

 and in direct contact with the Devonian. 



In Scandinavia the strata of the lower palasozoic rocks are of much 

 less thickness than in Bohemia, in Great Britain, and especially in 

 America. They average only about one thousand feet for the whole 

 series of the primordial and second fauna, instead of the ten and 

 twenty thousand feet of the English and American series. Further, 

 these strata have suffered numerous dislocations and breaks, which 

 have parcelled them out in small groups, on divers points, at some dis- 

 tance from each other. And to add still more to these difficulties, 

 great denudations, carrying after them enormous quantities of materials 

 transported by the great glaciers of the glacial epoch, have destroyed or 

 covered up all the strata, leaving merely some outcroppings here and 

 there, very difficult to class and to connect certainly with each other. 



* Faune Silurienne des Environs de Ho£ en Bavicrc, pp. 56, 57 (Prague, 



18G8). 



