NO. 1192. TRENTON FA UNA' OF BAFFIN LAND—SCHUCHEET. 175 



SUMMARY. 



The only Lower Silurian horizons known in northeastern Arctic 

 America are of Trenton and Utica age. The latter zone appears only 

 on the north shore of Frobisher Bay, but the Trenton is found in 

 various places from the north shore of Hudson Strait to latitude 81° 

 north. The Lower Silurian is thickest on Akpatok Island, where it is 

 from 400 to 500 feet in depth. Dr. Bell, however, estimates the entire 

 thickness of these strata in this region to be not less than 900 feet. 



In Baffin Land, and apparently elsewhere in Arctic America, the 

 Lower Silurian strata rests un conform ably on old crystalline rocks. 

 To the north of Baffin Land, the former are overlain by beds of Niag- 

 ara or Wenlock age. 



The Trenton faunas, occurring in various places around the insular 

 Archaean nucleus of North America, have much in common, and this 

 indicates that the conditions at that time were very similar, while the 

 sea was in communication throughout. As yet, however, the distri- 

 bution of the strata, together with their faunas, are well known only 

 to the south and southeast of the Archaean nucleus, yet that of the 

 west (Manitoba) and of the northeast (Baffin Land) show direct com- 

 munication. 



The Baffin Land fauna had an early introduction of Upper Silurian 

 genera in the corals Halysites, LyeJlia, and Plasmo])ora. In Manitoba 

 similar conditions occur in the presence of Halysites, Favosites, and 

 Dipliypliyllum. Other Upper Silurian types do not appear to be 

 present. 



The Trenton fauna of Silliinan's Fossil Mount, at the head of Fro- 

 bisher Bay, has seventy-two species, of which twenty-eight are 

 restricted to it. This fauna shows an intimate relationship with that 

 of the Galena of Minnesota, Iowa, and Wisconsin. Fifty-seven per cent 

 of the species of Baffin Land also occur in the Galena of the regions 

 just mentioned. 



The Trenton fanna of Baffin Land shows that the corals, brachiopods, 

 gastropods, and trilobites have wide distribution, and are therefore 

 less sensitive to differing habitats apt to occur in widely separated 

 regions. On the other hand, the cephalopods, and jDarticularly the 

 pelecypods, indicate a shorter geographical range. The almost complete 

 absence of Bryozoa in the Baffin Land Trenton contrasts strongly with 

 the great development of these animals in Minnesota and elsewhere in 

 the United States. 



