190 A. P. Coleman — Lower Huronian Ice Age. 



bowlders of the same rocks, granite, banded jasper, etc., makes 

 it very probable that they belong to the same age and have 

 had a similar origin. 



It is evident that for useful study the least metamorphosed 

 examples of the bowlder-bearing rock should be selected, such 

 as those of the typical Huronian region or those between Sud- 

 bury and Lake Temiscaming. 



In the western region I have never succeeded in loosening 

 stones from their matrix so as to observe whether the surfaces 

 were striated. Until recently the same difficulty was met in 

 the eastern conglomerates ; but the new silver mining district 

 at Cobalt has at last furnished a few pebbles and larger stones 

 which have preserved their original surfaces. 



The outcrops at Cobalt are well exposed and show the usual 

 variations of the so-called basal Huronian conglomerate. 

 There are some indefinite bands crowded with small stones, 

 often well rounded, while other parts of the outcrops have 

 very few bowlders or smaller stones, and these are often angu- 

 lar. The matrix varies from slaty material, sometimes with a 

 hint of stratification, to graywacke composed of coarse and 

 fine rock fragments, mostly quite unrounded. A few geolo- 

 gists have supposed, as was formerly suggested for the 

 Dwyka of South Africa, that the matrix is a basic eruptive 

 rock ; but its fragmental character is clearly seen in the field 

 and in thin sections. 



The enclosed stones' include large and small blocks of gran- 

 ite, many felsitic and porphyritic rocks, greenstones, and a few 

 bits of banded silica derived from the iron formation of the 

 underlying Keewatin. 



Professor Miller, who has mapped the region for the 

 Bureau of Mines of Ontario, guardedly suggests the resem- 

 blance of this rock to bowlder clay.* He calls attention to 

 the fact that " the granite bowlders are often two or three 

 feet or more in diameter and distant a couple of miles from 

 exposures of the rock " ; but on the whole seems opposed to a 

 glacial origin. 



By the exercise of care and patience it has been possible to 

 break from their matrix wholly or partially about twenty of 

 these stones, mostly only an inch or two in diameter, but half 

 a dozen from three to six inches across. As coarse-grained 

 rocks like granite seldom show distinct striations in modern 

 bowlder clays, felsites and fine-grained greenstones were 

 selected to work upon. Of the twenty stones four or five are 

 more or less striated, but only one is heavily and decisively 

 scored. Unfortunately the matrix could not be completely 



* Bur. Mines, 1905, p. 41. 



