8 G. F. MATTHEW ON TJ1J<; 



l)ail <j1' ihii North Atlantic Oceau, aud the Baltic and Mediteirauean Seas ; the other coA^ered 

 the Uuited States of America aud the southern part of Canada exclusive of Acadia. To 

 the north of these seas Prof. Marcou supposes there was a land barrier which extended 

 from the great lakes of North America to Ireland aud Scandinavia. 



Prof Marcou has the merit of having first formulated the regional distinctness of the 

 Cambrian faunas in America, but it seems to me that so perfect a land barrier as he 

 invokes was not necessary to divide them, in the view that differences of temperature in 

 the sea may have been equally efficacious. 



Prof. Marcou's papers do not fully discuss the whole Cambrian succession, but relate 

 chiefly to the Lower aud Middle Cambrian (called by him Lower aud Middle Taconic). 

 He considers that in the two marine regions above described which he calls the Acadio- 

 Russiau sea and the Nevado-Canadian sea, two diverse and independent faunas flourished 

 simultaueov^sly, aud that these faunas were separated by a narrow land barrier along the 

 Atlantic shore of the United States and Canada. 



Another writer, Mr. C. D. "Walcott, who has given a great deal of attention to the 

 Cambrian rocks, has lately written two works on this subject, published by the United 

 States Geological Survey.' They relate chiefly to the Olenellus zone, but describe also the 

 distribution of the whole Cambrian succession in North America. Mr. Walcott makes 

 some important generalizations, one to the effect that the " Lower and Middle Cambrian " 

 rocks (Olenellus aud Paradoxides beds) are absent from the central part of North America 

 (the Mississippi Valley). Another is that the Olenellus fauna was a coast fauna and 

 extended along the shores of a continental mass of land which included the region of the 

 Mississippi Valley and the great lakes of the St. Lawrence Basiu. He supposes that this 

 coast fauna was shut in and protected by a land barrier extending all along the Atlantic 

 shore, and another aloug the Pacific slope between the Rocky Mountains and the Sierra 

 Nevada. Within these barriers existed sounds or inland seas in which the Olenellus 

 fauua flourished. 



Mr. Walcott's view of the relation of land and sea in the interior of North America, 

 during the Cambrian age is thus quite at variance with that of Professor Marcou, who 

 supposes it to have been covered with a wide sea, tenanted by the fauna with Oleuellus. 



The bearing of these theories on the known facts relative to the diffusion and sequence 

 of the Cambrian faunas will appear more clearly as we take up the faunas in greater detail 

 and show their relation to the zones with graptolites. 



So large an area of the North American coutineut is covered with Post-Cambrian 

 rocks, aud in many areas where Cambrian strata actually appear, have metamorphism and 

 dynamical movements in the rock masses to so great an extent obliterated or obscured the 

 fossils, that data for determining the succession and distribution of the faunas is extreme- 

 ly scanty, aud too much localized. The views put forward in this paper, are therefore 

 rather for the purpose of directing attention to this subject, and of suggesting lines of 

 investigation, than with belief that they contain all the truth relative to this complex 

 and difficult problem in biology. 



' " The Fauna of the Lower Cambrian or Olenellus Zone," 1890, aud " Bulletin 81— Correlation Papers, Cam- 

 brian," 1891. 



