THE LOWER HURON I AN ICE AGE 151 



which was measured reaching diameters of 5X3X3 feet; but the 

 largest bowlder seen, near Temagami station, was of greenstone show- 

 ing pillow structure, having diameters of 8X5 ft. as exposed on an 

 ice-smoothed surface. Many of these bowlders are several tons in 

 weight and some of the granites are miles away from the nearest 

 known source. The smaller pebbles of felsite often show exactly the 

 same subangular shapes with irregular well-polished surfaces as are 

 found on pebbles of fine-grained rock in later bowlder clays. 



Fig. 2. — -Lower Huronian "soled" bowlder. 



In many parts of the tillite the stones are sparsely distributed, some- 

 times several feet or even yards apart, and the red granites stand out 

 sharply from the green-gray ground-mass. Such parts of the con- 

 glomerate present exactly the characters of till or ground moraine. 



THE MATRIX OF THE BOWLDER CLAY 



The matrix of the tillite is generally graywacke, fine grained, but 

 containing small angular particles of quartz and feldspar. It shows 

 no stratification as a rule, though the rock as a whole may have a 

 rude banding, pebbles and bowlders being more numerous in some 

 layers than in others. In the original Huronian region, as described 

 by Murray and Logan, the matrix was called slate, the rock being 



