XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 399 



Swedish rocks as given in the Lethsea Suecica in 1837, and not 

 as he had previously given it." (Ante, pages 366 and 395.) 



The concurrent evidence deduced from stratigraphy, from 

 geographical distribution, from lithological and from paleonto- 

 logical characters, thus led Logan, from the first, to adopt the 

 views already expressed by Bigsby, Emmons, and Bayfield, 

 and to assign the whole of the paleozoic rocks of the southeast 

 shore of the St. Lawrence below Montreal to a position in the 

 New York system above the Trenton limestone. While thus, 

 as he says, founding his opinion on the stratigraphical evidence 

 obtained in eastern Canada, Logan was also influenced by the 

 consideration that the rocks in question were continuous with 

 those in western Vermont. Part of the rocks of this region 

 had, as we have seen, originally been placed by Emmons at 

 this horizon, while the others, referred by him to his Taconic 

 system, were maintained by Henry D. Eogers to belong to the 

 Hudson Eiver group ; a view which was adopted by Mather 

 and by Hall, and strongly defended by Adams, at that time 

 engaged in a geological survey of Vermont, with which, in 

 1846 and 1847, the present writer was connected. 



As regards the subsequent paleontological discoveries in 

 these rocks in Canada, it is to be said that the graptolites 

 first noticed by Bigsby in 1827 were rediscovered by the 

 Geological Survey at Point Levis in 1854, and having been 

 placed in the hands of Professor James Hall (who in that year 

 first saw the rocks in question), were partially described by him 

 in a communication to Sir William Logan, dated April, 1855, 

 and subsequently at length in 1858. (Eeport Geol. Survey for 

 1857, page 109, and Decade II.) They were new forms, it is 

 true, but the horizon of the graptolites, both in New York and 

 in Sweden, was the same as that already assigned by Logan to 

 the Point Levis rocks. Thus these fossils appeared to sustain 

 his view, and they were accordingly described as belonging to 

 the Hudson Eiver group. 



Up to 1856 no other organic remains than the graptolites 

 and the two species of brachiopods noticed by Sir William 

 Logan were known to the geological survey as belonging to 



