34 GEOLOGICAL MEMOIRS. 



one c?iaracterize(i by a less predominance of silex. These two 

 groups he compares with corresponding lithological groups in 

 Bohemia ; but mentions the presence of two others in that country 

 whose absence in England does not, he thinks, invalidate his argu- 

 ment. These absent groups do in fact appear in other districts be- 

 sides Bohemia, and especially in France. 



But, without dwelling on this evidence, the fossils exhibit analogies 

 sufficiently striking in the palaeontological characters of the forma- 

 tions of the two countries. The identical species are not numerous, 

 being limited to Illcenus perovalis ; but the presence of the genus 

 Trinucleus peculiar to this part of the series, in Bohemia, as in 

 England, would be sufficient, the author thinks, to prove the con- 

 temporaneity of the beds containing it. He thinks it possible that, 

 on comparing good specimens, T. Caractaci might be identified with 

 T, ornatus of Bohemia. The Asaphus tyranmis and A, Powisii 

 of England are also analogues in dimensions of A. ingens and A, 

 nobilis, found in the quartzites of Bohemia. 



The JBellerophon, the Orthis, and the Conularia, already men- 

 tioned, give additional evidence in favour of the author's view ; and 

 he therefore concludes that his group (D) corresponds to the Caradoc 

 sandstone and the upper part of the Llandeilo flags. 



In France, as already observed by the author, there is no repre- 

 sentative of the group (C) ; but the present group (D) is abundantly 

 developed in Brittany and Normandy. The beds, as described by 

 MM. Dufrenoy and E. de Beaumont, agree exactly with the lower 

 members of this group. The author has received fragments from 

 these parts of the country, and identifies some few of the fossils ; 

 and he considers that the Lower Silurian beds of the north of France, 

 in which the Agnostus seems entirely absent, are of the same age as 

 the Bohemian group now under consideration. 



The Silurian rocks of Sweden having been already identified with 

 those of England by Sir R. Murchison, the author has no difficulty 

 in concluding that there also representative rocks exist. 



In concluding this sketch of the middle division, the author ob- 

 serves that two fossils, especially abundant and characteristic of the 

 English Caradoc Sandstone, absolutely fail in Bohemia. These are 

 Asaphus Buchii and TentaculiteSy of neither of which there has 

 yet been found the smallest trace. 



III. Upper Division. 



This is composed almost exclusively of calcareous beds forming 

 the exposed portion of the basin and surrounded by the dark- 

 coloured schists of the former group (C), which has been assimilated 

 to the Caradoc sandstone. The portion of the basin thus occupied 

 is of an elliptical form ; its longer axis (directed N.E. and S.W.) being 

 about 22^ English miles, and its shorter axis about 3| miles. It 

 extends from a little south of Prague to near the small town of 

 Zditz. There are also some small outlying patches. 



It would not be easy to account for this accumulation of all the 

 palseozoic limestones expanded to a great thickness in a nearly 



