154 A. P. COLEMAN 



From the outline just given it will be seen that every feature of the 

 Lower Huronian rocks has its close parallel in the complex of bowlder 

 clays and sediments of the Pleistocene, though the latter are, of course, 

 loose and unconsolidated. A comparison with the Dwyka conglom- 

 erate of Permo- Carboniferous times is more convincing still, since 

 the Dwyka is now solid rock. Hand specimens of the two tillites 

 might easily be interchanged by one not familiar with them. Speci- 

 mens from Matjesfontein in Cape Colony or N'gotsche Mountain in 



Fig. 4. — Polished pebbles in ancient till. Dwyka to left, Lower Huronian to 

 right. 



Natal placed beside specimens from Cobalt or north of Lake Huron 

 present the same fine-grained gray matrix with angular bits of quartz 

 and feldspar, or fragments of granite, or small polished pebbles of 

 felsite. As shown before, even thin sections under the microscope 

 present no material differences. 



In fact, the only important point of distinction between the two 

 tillites is the comparative ease with which the Dwyka matrix weathers, 

 setting free the inclosed stones ; while in the Cobalt rock matrix and 

 pebbles weather at nearly the same rate. In both tillites when fresh 

 it is hard to break out the stones by the hammer, since the fractures 



