228 



Pumpelly and Van Hise — Observations upon 



schist 



PEGMATITE 



crystalline schists. A gray granite-gneiss and a red granite 

 occurs in considerable masses, as do also dark colored schis- 

 tose rocks. Here the fine-grained gneisses and crystalline 

 schists have been most intricately intruded by the granite, 

 and later still both have been cut through and through by 

 pegmatitic granite. In passing from a granitoid exposure to 

 a schist exposure the first evidence of the schists is the appear- 

 ance of angular and partly rounded inclusions of these rocks. 

 In passing onward there appear very numerous blocks of the 

 schist which have been free to move, and the laminations of 



which strike in vari- 

 ous directions, al- 

 though there is often 

 a rough parallelism 

 in their structures. 

 (See figure 1, drawn 

 from a photograph.) 

 The schistose blocks 

 have been more or 

 less absorbed and the 

 whole has a pseu- 

 do-conglomeratic ap- 

 pearance which is 

 identical with pseu- 

 do-conglomerates of 

 a"similar origin described by Lawson about Rainy Lake.* In 

 passing onward towards the schistose area the intrusive granite 

 has cut across the lamination of the schists and parallel to them 

 so as to make a network of intrusive dikes ; but the schistose 

 material has not greatly moved from its original position, con- 

 sequent upon which there is a parallelism of structure. In 

 passing still onward the schists are cut by veins or dikes of 

 granite, but in subordinate quantity, and finally the continu- 

 ous schists are found (lower part of fig. 3.) No observing 

 geologist would take these intrusive relations and pseudo- 

 conglomerates to indicate that the schists are later than the 

 granite-gneiss. Such doubtless are the relations described by 

 Barlow,f as a consequence of which he drew the conclusion 

 that nowhere on the north shore of Lake Huron are any detri- 

 tals which are later than and rest unconformably upon the 

 basement complex. If we understand his descriptions, he re- 

 gards the dark-colored crystalline schists as Huronian, whereas 

 they are really pre-Huronian. Seeing facts of one kind and 



* Report on the Geology of the Rainy Lake Region, Andrew C. Lawson, Geol. 

 and Sat. Hist. Survey of Canada, vol. iii, 1887, pp. 130F-139F. 



f On the Contact of the Huronian and Laurentian Rocks North of Lake Huron, 

 Alfred E. Barlow: Am. Geol., 1890, vol. vi, pp. 19-32. 



GRANITE 



