EARLY PALEOZOIC BRYOZOA OP THE BALTIC PROVINCES. 35 



reason for believing that the Lowville, Black River, Trenton, and 

 Richmond rocks are actually present in the section as for assuming 

 that only Trenton strata occur. The former view is strengthened 

 by the unquestioned stratigraphy of areas further south and west. 

 Ulrich's identification of recent collections made by Kandle in Alaska, 

 has shown the occurrence of a Black River fauna followed by a coral 

 fauna of Richmond age. In Manitoba and elsewhere in Canada, the 

 early Trenton strata (Maclurea bed) are succeeded by the Earliest 

 Silurian Richmond group. The same succession of Richmond strata 

 upon Trenton or older rocks is present in various parts of the Rocky 

 Mountain area of the United States, especially in the Big Horn Moun- 

 tains, and even as far south as El Paso, Texas. The most prevalent 

 zone of the Richmond group contains numerous corals of Silurian 

 genera, Halysites, Lyellia, Plasmopora, and Odlapmcia. Tliis is the 

 same fauna noted on other pages of this work as present in the upper 

 Lyckholm and Borkholm limestone of Baltic Russia. The 11 "Cin- 

 cimiatian" species recorded by Schu chert from Silliman's Mount 

 includes this same coral fauna, and it therefore seems certain that 

 the Richmond group is represented in the section. The Richmond 

 age of these corals was further evidenced by the fact that two very 

 characteristic brachiopods, a variety of PlatystropJiia acutilirata and 

 of Plectambonites sericeus came to light when I carefully searched a 

 fragment of limestone adhering to one of the corals. This particular 

 variety of Plectarribonites is highly characteristic of the Richmond in 

 America and Europe. It is distinguished by the occurrence of small 

 teeth along the edge of the cardinal area of the dorsal valve. 



The 38 strictly Trenton species, when compared with Minnesota 

 faunas, are found to be characteristic of the Clitamhonites, Nemato- 

 pora, and Maclurea beds of the Minnesota-Iowa composite section, 

 or, in other words, probably occur in strata equivalent to the early 

 Trenton (Stewartville and Prosser limestone) of the more southern 

 area. The species of Fusispira, Maclurea, Maclurina, Receptaculites, 

 IscTiadites, and other genera listed by Schuchert as occurring in the 

 Silliman's Mount fauna, and elsewhere only in the Minnesota Trenton, 

 are associated with a gray, fine grained rock which, when carefully 

 prepared, furnished a small fauna of Ostracoda including a Leperditia 

 with Trenton afiinities, but more especially the two bryozoans char- 

 acteristic of the Nematopora bed in Minnesota, Nematopora ovalis 

 Ulrich and PacJiydictya pumila Ulrich. 



Concerning the occurrence of Lowville limestone at Silliman's 

 Fossil Mount, the evidence is not as conclusive as that for the Lower 

 Trenton and Richmond divisions, indeed, it is probable that only the 

 equivalent of the Decorah shale is present since the 10 Lowville 

 species listed by Schuchert occur also in that formation. Schuchert's 

 list, however, shows enough characteristic Black River species to 



