MIDDLE AND UPPER ORDOVICIAN. 223 



Baffin Land such are not known to be present. Here, then, there seems to be a complete 

 break from the Laurentian to -the Trenton, followed by another break paleontologically, in the 

 absence of the Cincinnatian beds and probably the lower horizons of the Upper Silurian. The 

 Lower Silurian fossils of this area indicate nothing older than the typical Trenton of New 

 York and the Galena of Wisconsin and Minnesota," and nothing younger than the Utica stage 

 of the United States. The thickness of these beds is not less than 900 feet and probably 

 exceeds this. 



Schuchert cites lists of fossils collected by Hall and described by Stevens ^'^ 

 and Emerson ^^* and gives a new list of 72 species from Silliman's Fossil Mount 

 and their distribution according to horizons (Lowville, Black River, Trenton, and 

 Cincinnatian) and according to regions (Minnesota-Manitoba, New York-Ottawa). 

 He concludes : ''^^ 



From Mr. Porter's description, it will be seen that the fossils recently collected at SiUi- 

 man's Fossil Mount are from various horizons, and yet there is nothing to indicate the presence 

 of more than one fauna. The foregoing list shows that at present there are 72 species known 

 from this locaUty, and of these 28 are restricted to it. There are, therefore, 54 species which are 

 common to other locahties, a goodly number with which to make safe correlations. Of these 

 54 species, 41, or 57 per cent of the known fauna, are also found in the region of Minnesota, 

 Wisconsin, and Iowa, while 17 are known to occur in New York and Ottawa. 



On comparing the 54 widely distributed species with those from definite stages in Minne- 

 sota, it is seen that 10 are also found in Birdseye (Lowville), 17 in the Black River, 38, or about 

 70 per cent, in the Galena, the direct equivalent of the New York Trenton, and 11 in the 

 Cincinnatian group. 



From these figures it is evident that the stage of Silhman's Fossil Mount belongs in the 

 Galena, and that the fauna is more intimately related to that of the. Minnesota region than to 

 the Trenton of New York. When the New York Trenton fauna is restudied in the light of 

 recent researches in Minnesota,* however, it will be shown that the two faunas have more in 

 common than now appears. On the other hand, the hthological similarities of the Minnesota 

 Galena and Silliman's Fossil Mount, Ught-colored shales predominating in both areas, may 

 explain in large measure the close identity of these widely separated faunas. 



Schuchert ^^^^ closes his paper with the following sunamary of the information 

 available on the Arctic Ordovician: 



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 Tren- 

 ton 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. BeU, 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 

 rest unconformably on old crystalUne rocks [except where Cambrian is present in the far north; 

 see p. 155]. To the north of Baffin Land the former are overlain by beds of Niagara or Wen- 

 lock age. 



The Trenton faunas, occurring in various places around the insular Archean 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 dis- 

 tribution of the strata, together with their faunas, are well known only to the south and south- 

 east of the Archean nucleus, yet that of the west (Manitoba) and of the northeast (Baffin Land) 

 show direct communication. 



" See Cambrian of Bache Peninsula, Chapter III, p. 155. 



6 Paleontology of the Lower Silurian fossils of Minnesota: Geology of Minnesota, vol. 3, pts. 1 and 2, Geol. Nat. 

 Hist. Survey Minnesota, N. H. Winchell, State geologist. 



