EAELY PALEOZOIC BEYOZOA OP THE BALTIC PROVINCES. 7 



A number of authors have attempted correlations of the Russian 

 Cambrian and Ordovician rocks with the North American sequence, 

 but the ideas of most of these are reflected in the foUowing table 

 adapted from Credner's tables on pages 397 and 420 of his "Ele- 

 mente der Geologic:" 



Table of Cambrian and Ordovician strata. 

 [Adapted after Credner.] 





Baltic Russia. 



North America. 



Lower Silurian. 



Pent, borealis beds 



Hudson River shale. 

 Utica shale. 



Raikiill beds 



Borkholm beds 





Wesenberg beds 





Brandschiefer 



Echinospherites limestone 







(Trenton limestone. 

 ■^ Black River limestone. 

 [Birdseye limestone. 





Glauconite limestone and sands 



Chazy limestone. 





Dictyonema shale 



Calciferous sandstone. 





Obolus sandstone to the lowest con- 



/Potsdam group. 



\St. John (Acadian) group. 







Blue clay to the top of the Olenellus 

 mickwitzi zone. Lower sandstone. 



Georgia group (Olenellus series). 



The basis for correlation of the Ordovician portion of this table is 

 rather difficult for the American student to determine. Probably 

 there is none other than an arrangement of the formations in the two 

 areas upon the supposition that corresponding strata are or should 

 be present in each. 



Probably the best expression of opinion as to tliis correlation is 

 that given in the table on page 8, translated from Kayser's tables, 

 pages 74 and 119 of his "Lehrbuch der Geologic," 1908, although this 

 offers the same objection. Here, however, the identification of the 

 strata ranging from the Orthoceras (Vaginaten) limestone to the 

 Wesenberg, with the Mohawkian, and the Lyckholm-Borkholm 

 series with the Cincinnatian, is more in line with the results brought 

 out from a study of the bryozoan faunas. 



