CORRELATIOX OF SILURIAIs 367 



that Silurian rocks are present farther south on Little Current, Drown- 

 ing, and other branches of the Albany River. 



Fragments of yellow dolomite containing the fossils Favosites favosus, 

 Stropheodonta acantlioptera, Stropheodonta sp., of. Yirgiana decussata, 

 Pterinea occidentdlis, and Leperditia Jiisingeri var. were found in the 

 glacial drift along Xelson River 50 miles above the nearest exposure of 

 Paleozoic rocks farther down that stream. 



CORRELATION OF THE SILURIAN FORMATIONS OF THE HUDSON BAT REGION 



In general. — The Port Nelson and Severn River limestones in the 

 Hudson Bay region are thought to represent the pre-Niagaran or Alex- 

 andrian series of the Silurian system, while the Ekwan River limestone 

 and the Attawapiskat coral reef are referred to the Niagaran. 



Port Nelson limestone. — The most characteristic fossil of the Port 

 ^NTelson limestone in the Hudson Bay region is Yirgiana decussata. This 

 species also occurs abundantly in the basal Silurian rocks at the Grand 

 Rapids of Saskatchewan River,^® and it is practically certain that the 

 strata from which they came in the two regions represent the same strati- 

 graphic horizon. The Port Nelson limestone includes all of the Silurian 

 strata in this region below the top of the layers containing Yirgiana 

 decussata. In another paper^' the senior writer has shown that the 

 lower part of the Silurian limestone in the Hudson Bay region, contain- 

 ing shells of Yirgiana decussata, corresponds with the zone containing 

 numerous shells of this species at the Grand Rapids of Saskatchewan 

 River, and was to be correlated with the basal part of the Stonewall lime- ' 

 stone of Manitoba and with the upper part of the Ma3^ville limestone in 

 Wisconsin and northern Michigan. It probably represents the same 

 period of deposition as the early Silurian strata of western and north- 

 western North America, which contain numerous shells of Yirgiana that 

 have previously been referred to the genus Conchidium or Pentamerus. 



Severn River limestone. — The Severn River limestone clearly corre- 

 sponds with the Silurian limestone described by Hume from the Lake 

 Timiskaming region and correctly correlated by him with the Cataract 

 formation of southern Ontario. It corresponds with that part of the 

 Stonewall limestone of the Grand Rapids of Saskatchewan region above 

 the zone of Yirgiana decussata and is considered the equivalent of the 

 Hendricks and Fiborn limestones of northern Michigan. The correlation 



^6 E. M. Kindle : Notes on the geology and paleontology of the lower Saskatchewan 

 River valley. Geol. Survey of Canada, Mus. Bull. no. 21. Geological series no. 30, Octo- 

 ber 14, 1915, p. 16. 



" T. E. Savage : Correlation of early Silurian rocks of the Hudson Bay region. Jour- 

 nal of Geology, vol. 26, no. 4, 1918, pp. 334-340. 



