1006 THE GEOLOGY OP MINNESOTA. 



[Conglomerate. 



had an abundant source of supply. It is also evident that, in part at least, they 

 were already silicified. They must have been derived from rhyolytes more or less 

 silicified (or jaspilytes) which previously covered the Archean, and which can be seen 

 lying on the Archean at the west end of Grunflint lake, at the east side of Black 

 Fly bay. 



Taken together the sections of rocks Nos. 1689, 433H and 436H afford an impor- 

 tant demonstration, viz.: That in one direction the rock taconyte grades into a fine 

 black flint, and in the opposite direction into a conglomerate in which the globular 

 masses increase to pebbles over an inch in diameter. This shows that these rocks 

 had the same source, as the microscope shows that they have the same composi- 

 tion. N. H. w. 



X 



" / 



