THE LOWER SILURIAN AREA. 69 



the river. Farther north Lower Silurian rocks are exposed on many of the 

 islands of Lake Winnipeg and along its western shore, but no exposures of 

 the underlying Cambrian beds, which are penetrated by the artesian well 

 at Grafton, N. Dak., have been found in this region. Against the western 

 border of the folded and eroded Archean rocks the Lower Silurian forma- 

 tions repose with nearly horizontal stratification. Their general dip, vary- 

 ing fi'om a few feet to 10 feet or more per mile, is westward, at right angles 

 with the axis of Lake Winnipeg and the line of junction of the Archean 

 and Paleozoic rocks. 



Descriptions of the outcrops of Silurian and Devonian strata in Mani- 

 toba will prepare us to consider afterwards the sections of artesian wells 

 farther south, which give evidence that Silurian formations immediately 

 underlie the drift upon a large portion of the Red River Valle}', on both 

 sides of the international boundary and of the river, where no rock expo- 

 sures exist. 



Outcrops on Lake Winnipeg. — Near Grindstone Point, on the west side 

 of Lake Winnipeg, 60 miles north from the south end of the lake. Hind 

 observed a section of 18 feet of level limestone overlying 20 feet of sand- 

 stone, and refers it, upon the e-sddence of its fossils, to the Chaz}' epoch.^ 

 Beds of limestone, shale, and sandstone are also described by Hind on Deer 

 Island, about 8 miles south of Grindstone Point, being apparently the same 

 strata as at that locality; and Panton reports an extensive outcrop of lime- 

 stone on the west part of Big Island, a few miles east from Deer Island, 

 and other exposures of the same on Punk Island, 3 or 4 miles to the north. 

 Black Bear Island, a few miles northwest from the Narrows at Dog Head, 

 and Berens or Swampy Island, about 40 miles farther north, also contain 

 low outcrops of limestone, -which Panton, who refers them to the same 

 formation with the foregoing, found sparing-lv fossiliferous on the former 

 but richly so on the latter of these islands.^ 



'Report of the Assiniboine and Saskatchewan Exploring Expedition, 1859, p. 86. These beds 

 seem equivalent with the well-defined limestone stratum, about 30 feet thick, richly fossiliferous, 

 which has been commonly called the Trenton limestone in southeastern Minnesota, Ijut which is 

 recently referred by Mr. E. 0. Ulrioh to the Chazy or perhaps the Black River formation (Geol. and 

 Nat. Hist. Survey of Minn., Fourteenth Annual Report, for 1885, p. 57). 



-"Xoteson the geology of some islands in Lake Winnipeg,'" by J. Hoyes Panton. Transactions 

 of the Historical and Scientific Society of Manitoba, January 28, 1886. 



