52 



Minnesota Academy of Science 



Fig. 11. — Secondary Jaspilyte. Upper Keewatin, Tower. 



evidently derived as a debris from the great greenstone. The 

 strata of this schist stand nearly vertical, but non-conformable on the 

 greenstone just mentioned. 



THIRDLY, A great series of other fragmental rocks, some very 

 fine and some coarse. Many of these strata can be called gray- 

 wacke, and many others are as fine as slate, and even as flint. 

 These sediments sometimes appear like quartz porphyry. 



While these are the principal types of the rocks in this forma- 

 tion, they are not always distinct and plainly characterized, but they 

 grade mto each other with all conceivable intermixtures. Some- 

 times the green schist element in the form of chlorite is mixed with 



