40 GEOLOGICAL MEMOIRS. 



Cambrian system (as modified in 1845)... Azoic. 



Lower Silurian system "I j^^^ •rj?^^^ 



Upper Silurian system | Fossiliferous. 



5. The azoic divisions in the two countries may be considered to 

 correspond in point of age, both from the nature of the rocks and 

 from their position. 



6. The middle divisions which are fossiliferous are comprised in 

 both districts between two geological horizons, characterized by 

 including the genera Battns and Trinucleus, These two horizons 

 are especially distinct in Bohemia, in consequence of the great thick- 

 ness of the group D, of quartzites or Caradoc sandstones. In both 

 countries there is an abrupt and total change in the palaeozoic fauna, 

 immediately above the horizon of the Trinucleus. 



This coincidence is considered by the author to establish the 

 identity of the middle divisions of Bohemia and England. 



7. The author considers, that the analogies that exist between the 

 palaeozoic faunas of England and Bohemia demonstrate, in spite of 

 irregularities in the development of certain families, that the Upper 

 Silurian series of England, and the three calcareous groups of Bohe- 

 mia, were formed during the same portion of the palaeozoic epoch. 



8. He believes, therefore, that taking for the terms of comparison 

 the three grand divisions sketched out, the central basin of Bohemia 

 represents in the same order as that traced in England, the succession 

 of the three great Silurian periods. 



9. Having established this resemblance and identity, the author 

 proceeds to the subject of the diversity recognizable in countries 

 remote from one another, and offers in a series of tables, a compari- 

 son of the fossils of the two countries for the three periods. He 

 then concludes, that there is a complete correspondence between the 

 three great divisions of the Silurian system in Bohemia and Britain ; — 

 that from a detailed comparison of the local faunas, it appears that 

 the different groups in the two countries do not correspond; — that the 

 Silurian system has therefore unity as a whole, but a diversity in detail; 

 and lastly, that this unity and diversity are everywhere to be remarked 

 in nature, and equally characterize the works of the Creator. 



General View of the Silurian Fauna of Bohemia, 

 Fishes. (Ichthyodorulite fragments) 1 



c™stacea.{™»Sdr;.::::;:;::::::::;;::::::::^?? 



Ileteropoda 5 



Cephalopoda 150 



Gasteropoda » 50 



Brachiopoda 100 



Monorayaria 9 



Dimyaria 100 



Encrinites 2 



Corals,&c 44 



Total 600 



Note. This table is made out from the specimens in the author's collection. 



[D. T. A.] 



Mollusca. 



