262 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



on the Saskatchewan, consists of 54 feet of white or yellow limestone, partly mag- 

 nesian, partly chalky, and partly ripple-marked and containing impressions of salt 

 crystals. The base is not seen, but limestone of Trenton age lies not far below. 

 Fossils are lacking in the lower 10 feet but numerous above, and the strata are 

 compared by Tyrrell ^^^* with the lower part of the Niagara of Wisconsin. Above 

 the lower portion is a considerable thickness, "possibly a few hundred feet," of 

 dolomites and dolomitic limestones of upper Niagara age. The beds exhibit impres- 

 sions of salt crystals and are in some places " fragmental." T5T:Tell gives a list of 41 

 species of fossils determined chiefly by Whiteaves. Near Lake St. Martin (latitude 

 51° 45') the strata of Niagara age rest on granite of an island in the rocks of Trenton 

 age, which elsewhere underlie them. Gypsum occurs not far away. Near by, on 

 the eastern shore of Lake Manitoba, "the thin-bedded upper Niagara dolomites 

 are overlain by a few feet of a thick-bedded massive stromatoporoid magnesian 

 limestone, which yielded a few corals, including Pycnostylus guelphensis." 



N-O 8. SOTTTHEASTERN ALASKA. 



The Wales "series" of southeastern Alaska comprises argillites, of great thick- 

 ness but unknown age, and younger limestone, 2,000 feet or more thick, from which 

 Kindle *^^ lists Silurian fossils. He says: 



Two horizons of the Silurian have been recognized. The older of these is represented 

 by a small fauna which has been found on the northwest coast of Kuiu Island. In the lime- 

 stones northeast of Mead Point the following fauna occurs: 



Diphyphyllum? sp. 



Conchidium knighti (Sow.). 



Whitfieldella sp. 



Holopea cf . semis Barr. 



Murcliisonia sp. , 



None of the species are abundant, with the exception of C. TcnigMi, which is represented 

 by great numbers of large shells in one thin bed of limestone. 



C. TcnigMi is one of the characteristic fossils of the Aymestry limestone of the Ludlow 

 group of England. It is known also from Russia and Bohemia. There appear to be no 

 authentic records of its occurrence in the Silurian faunas of the United States. The nearest 

 equivalent of this fauna in eastern America is the Niagara fauna. While none of the species 

 collected are identical with Niagara species, Conchidium TcnigMi is very closely related to 

 C. nysius of the Niagaran fauna. 



The Kuiu Island fauna occurs in the midst of a limestone series which appears ta be 2,000 

 feet or more in thickness. Other portions of the series which were examined appeared to be 

 barren. Upward these limestones seem to terminate with volcanic breccias, while below they 

 pass into cherts and argillites of undetermined age. 



The later Silurian horizon does not appear to be present in the Kuiu Island section. It 

 occurs at Freshwater Bay, where more than a thousand feet of gray limestones, which precede 

 the beds carrying Devonian fossils, outcrop along the south side of Freshwater Bay. The 

 lower two-thirds of this series comprises dark-gray, thinly laminated limestones. Leperditias 

 of an undetermined species occur a,bundantly in certain beds in the lower part of the series. 

 A few fragments of another and larger crustacean, probably a Ceratiacaris, are associated with 

 them. These crustaceans comprise the fauna of the lower 700 feet of the section, so far as 

 discovered. 



In the upper 300 feet of the limestones of the section a crustacean fauna predominates, 

 but the types represented are unlike those of the preceding division. One of the conspicuous 

 forms in this fauna is a largely undescribed ostracod provisionally referred to Isochilina by 



