648 EDWARD STEIDTMANN 



the Nipigon area, the Onaman Iron Range, and the Seine River in 

 the Rainy Lake district. The Sudbury series he regards as being 

 partly a delta deposit laid down in a moist cool climate, but finds 

 it strange that carbon is lacking. In the interval between Sud- 

 burian and Huronian time, the area was folded and eroded to a 

 surface very much like that of the present Canadian Shield. 



For the nature of the Lower Huronian, he refers to Logan's 

 type section on the northeast coast of Lake Huron. TilHtes are a 

 characteristic constituent of the Huronian, but in addition it con- 

 tains stratified deposits. Other Lower Huronian areas are found 

 in the Larder Lake, Chibougama, and Steep Rock Lake districts. 

 The Lower Huronian rocks have a marked unconformity at their 

 base, but are in general less severely folded than the Sudbury 

 series. At the start the chmate of the period appears to have 

 been cool and glacial. The existence of animals is suggested by 

 the occurrence of limestone. 



The Animikie he characterizes as a period of great submergence 

 during which great quantities of iron compounds and black slates 

 were deposited. 



The Keweenawan of the Canadian Shield rests upon the eroded 

 Animikie. It includes three series, of which the two lower are 

 chiefly sedimentary, while the upper is largely volcanic. The 

 sediments consist largely of sandstones and conglomerates, charac- 

 terized by red color and absence of carbon. The volcanics are 

 chiefly basic flows, but possibly include some felsites and por- 

 phyries. Dikes are common, but as yet no definite volcanic vents 

 have been found. Other areas of the Canadian Shield probably 

 containing Keweenawan are the Nastapoka and Manitaunick 

 Islands, Central Labrador, and the south side of Hudson Straits, 

 the regions of Lake Athabasca, Great Slave Lake, and the area 

 between the east side of Great Bear Lake along the Copper Mine 

 River northward to the Arctic Ocean. Deposition during Kewee- 

 nawan time, according to Coleman, was chiefly on the land in a 

 warm dry climate. He speculates as to the source of great quan- 

 tities of lavas and relates the development of the Lake Nipigon, 

 Sudbury, and Lake Superior basins to the collapse of the surface 

 resulting from the extrusion of the lavas. 



