ELY GREENSTONE. 161 



This has resulted in the formation of minerals with higher specific gravity" — 

 hence such as occupy less space — and produced an arrangement of these 

 minerals which makes them conform to the law of the production of 

 secondary minerals in schists, as explained by Leith.'^ Moreover, the great 

 additional space within this portion of the earth's crust which was required 

 by the intrusion of the granite has been partly supplied by this very change 

 of the preexisting greenstones into related rocks that occupy less volume. 

 In their formation, pressure has, of course, been a very important factor; 

 hence the more frequent occurrence among them of schistose forms of 

 rocks. 



CONTACT EFFECT OF GABBRO ON ELY GREENSTONE. 



In thi-ee areas the Archean Ely greenstone lies in juxtaposition with 

 gabbro of Keweenawan age. A contact of the greenstone with the gabbro 

 occurs east of Disappointment Lake, in sees. 26 and 35, T. 64 N., R. 8 W. 

 Here the anticline of Ely greenstone has been cut across on its east side by 

 the gabbro. Another contact occurs in sees. 1 and 2, T. 64 N., R. 6 W., at 

 the southwest side of Gobbemichigamma Lake. From sec. 2,5, T. 65 N., 

 R. 5 W., eastward through sees. 30, 29, 28, and 27, T. 65 N., R. 4 W., we 

 find an Archean anticline which is not in contact with the gabbro, being 

 separated from it by a minimum distance of perhaps 200 paces and a 

 maximum distance of half a mile. The greenstone has been metamorphosed 

 by the gabbro, although it has not been affected nearly so extensively as it 

 is where it is in contact with the granite.. Macroscopically no great 

 difference can be observed between the metamorphosed and the 

 unmetamorphosed greenstones. They are in all cases massive rocks, 

 and the metamorphosed portions appear to have essentially the same 

 characters as the remaining unmetamorphosed portions, although the 

 former weather somewhat more readily than the latter and have a 

 rusty brown color. 



The effect of the gabbro on the greenstone in j^roducing 

 metamorphosed rocks can be best seen in exposures on the west side 

 of Gobbemichigamma Lake in the sections above mentioned, on 



a Metamorphism of rocks and rock flowage, by C. E. Van Hise: Bull. Geol. See. Am., Vol. IX, 

 1897, p. 291. 



b Manuscript. 



MON XLV — 03 11 



