356 A. p. COLEMAN GLACIAL PERIODS AND GEOLOGICAL THEORIES 



conclusions as the present writer. Professor Miller, who has mapped the 

 Cobalt region, calls attention to the resemblance of the rock to boulder 

 clay, since "the granite boulders are often 2 or 3 feet or more in diameter 

 and distant a couple of miles from exposures of the rock."^^ Professor 

 Brock, who has described the gold-mining region of Larder lake, in the 

 same formation, but 20 miles farther north, gives the following account 

 of the rock : 



"The thickness and widespread extent of the conglomerate in northern On- 

 tario, where its general characteristics seem to remain constant throughout, 

 the clean-swept and often rounded surfaces of the older roclis on which it is 

 frequently laid down, and the extraordinary variation in the size of the boul- 

 ders — these and other facts stated above regarding the conglomerate of Larder 

 lake furnish the strongest evidence yet found for a glacial origin. But there 

 are still difficulties in the way of its acceptance. The deposits can not be said 

 to have the appearance of glacial deposits. Thei-e has been no boulder clay 

 recognized — ^the material has been at least resorted."^ 



If Professors Miller and Brock had been familiar with ancient glacial 

 deposits, such as the Dwyka in South Africa, they would no doubt have 

 taken a different view of the matter, since the Cobalt conglomerates are 

 exactly like the more consolidated varieties of the Dwyka conglomerate. 

 That some of the matrix shows hints of stratification is, of course, not an 

 argument against a glacial origin, for Pleistocene boulder clays and kame 

 deposits often show the same mixture of ice-formed and water-laid 

 materials. 



The vast extent of the Lower Huronian conglomerate is only explicable 

 by glacial action. In the east, near lake Chibougamou, Eichardson de- 

 scribed such a conglomerate, with boulders tons in weight, many years 

 ago;^* and similar conglomerates occur in every Huronian area mapped 

 in northern Canada through a region 1,000 miles long from east to west 

 and 750 miles broad. The only similar boulder-bearing formations known 

 are the Permo-Carboniferous and Pleistocene boulder clays, the Lower 

 Cambrian beds being apparently much less extensive; and those who 

 object to the interpretation should explain how these boulder beds hun- 

 dreds of feet thick, stretching over hundreds of thousands of square miles, 

 were formed if not by the action of land ice. 



Interglacial Periods in the Pleistocene 

 The four great glacial periods briefly outlined above are generally 



^ Bureau of Mines, Ontario, 1905, p. 41. 



38 Ibid., vol. xvi, part 1, p. 212. 



»» Geological Survey of Canada, 1870-1871, pp. 293-294. 



