A. P. Coleman — Lower Huronian Ice Age. 191 



removed from this one, but the exposed surfaces show the 

 striatums well on one face and distinctly on two others. 



Several of the smaller pebbles have the peculiar some- 

 what uneven but well polished faces with rougher corners so 

 often seen in the smaller stones of bowlder clay. 



Though the number of stones available is small, the propor- 

 tion showing more or less striation is as large as in recent 

 bowlder clay and all the usual features of ice-carved stones 

 are found in them. It may be added that they were taken 

 from undisturbed parts of the formation with no faulting to 

 cause slickensides, and that the stones themselves had not been 

 squeezed nor broken in the matrix. 



No striated surfaces were found where the conglomerate 

 rested on the underlying Keewatin ; but the only contact of 

 the two rocks examined was unfavorable for displaying such a 

 surface. Mining operations show that the rocks beneath the 

 Huronian have on the whole an uneven, somewhat undulating- 

 surface of low hills and valleys, the conglomerate often more 

 or less filling in these valleys. 



In the silver region the Lower Huronian has a maximum 

 thickness of about 500 feet so far as known. There are also, 

 as shown by Prof. Miller, conglomerates in the next overlying 

 formation, the Middle Huronian. 



The evidence for a Lower Huronian Ice Age may be 

 summed up as follows : 



A peculiar rock consisting of graywacke or finer materials 

 showing little or no stratification but containing pebbles or 

 stones, sometimes crowded, but more often scattered a few feet 

 apart, is found from point to point over an area 800 miles 

 long by 250 miles broad. The stones are of all sizes up to 

 diameters of several feet and of all shapes from rounded to 

 angular, many being subangular with rounded corners. The 

 stones are of several different kinds, some fragments of the 

 immediately underlying rock, others having a distant source. 



In the Cobalt mining region a few polished and striated 

 stones have been broken out of the matrix. They are closely 

 like stones from the Pleistocene bowlder clay of the same 

 region except that they lack the Niagara limestones of the 

 recent drift. 



Hand specimens of matrix and enclosed pebbles are pre- 

 cisely like the Dwyka tillite or conglomerate of South Africa, 

 which is undoubtedly of glacial origin. 



Against the glacial theory is the fact that no roches mou- 

 tonnees have yet been found on the underlying Keewatin 

 rocks. All the positive evidence is favorable to the theory of 

 glacial action as the cause of these curious bowlder-strewn 

 rocks. 



