290 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



"The pc])blcs or bowlders are in many cases subangular or sharply angular and are found 

 miles away from any known source; and as they may be of any size up to blocks weighing tons, 

 and are frccjuently very sparsely scattered through an unstratified matrix, a stone or two in 

 several yards, one can not help suspecting that the transporting agency was ice rather than water. 

 There are parts of the formation where the pebbles or stones are well rounded and crowded in 

 certain bands. In such cases they are probably true water-formed conglomerates; but the 

 prevalent type of the rock with scattered subangular stones or bowlders should not be called a 

 conglomerate, any more than a Pleistocene bowlder clay would receive that name. The appear- 

 ance of these so-called slate or graywacke conglomerates is closely like that of the Dwyka Ijowldcr 

 clays, for which Penck suggests the term 'tillite'; * * * rocks of the kind are found from 

 point to point across all northern Ontario, a distance of nearly 800 miles, and from the north shore 

 of Lake Huron in latitude 46° to Lake Nipigon in latitude 50°. 



"The more schistose of these conglomerates have their pebbles flattened and rolled out into 

 lenses not at all suggesting glacial action; but the fact that all of them, whether schistose or un- 

 modified, occupy, so far as known, the same position, immediately over the Keewatin, and con- 

 tain pebbles ancl 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. * * * 



"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 3 to 6 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 removed from this one, 

 but the exposed surfaces show the striations well on one face and distinctly on two others. 



"Several of the smaller pebbles have the peculiar somewhat 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 proportion showing more or less stri- 

 ation 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 shckensides, 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. 

 [Such are now known in three places and were described in 1912.] 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 loss filling in these valleys. * * * 



"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 precisely like the Dwyka tillite or con- 

 glomerate of South Africa, which is undoubtedly of glacial origin. 



"Against the glacial theory is the fact that no roches moutonnees have yet been found on the 

 underlying Keewatin rocks. AH the positive evidence is favorable to the theory of glacial action 

 as the cause of these curious bowlder-strewn rocks. 



" If the evidence given above is accepted, the occurrence of glaciation is probable over an area 

 too large to be the work of merely local mountain glaciers, and one must assume the presence of 

 ice-sheets comparable to those which formed the Dwyka. 



" The Lower Huronian is the second formation in the geological succession in North America, 

 only the Keewatin coming before it; so that the probable action of ice on a large scale is pushed 

 back almost to the beginning of known geological time. This implies that the climates of the 

 earlier parts of the world's history were no warmer than those of later times, and that in Lower 

 Huronian times the earth's interior heat was not sufficient to prevent the formation of a great 

 ice-sheet in latitude 46°" (1907: 188-92). 



