THE GEOLOGY OP MINNESOTA. 



[Green sehist. Graywacke. Argillyt*. 



No. 2270. GREEN SCHIST. (Ferruginous.) 



At the summit of the large island in Moose lake crossed by the section line between sees. 28 and 29, T. 64-9. 

 Ref. Annual Report, xxiv, page 81. 



Meg. Has a bright-green, weathered surface, rough with siliceous projections 

 from between which some softer mineral has been weathered out. It is charged, 

 within, with carbonate of iron which on oxidizing does not stay so as to stain the 

 weathered surface. The superficial green color fades out in other places, and the 

 surface is more or less rusty, the interior being gray. It is cut by a rather fresh 

 diabase dike four feet wide and by a narrow, vein-like quartzose dike of fine red 

 granite. No section. 



Age. Lower Keewatin(?) N. H. w. 



No. 2271. GRAYWACKE. f Siliceous, ferruginous. ) 



Part of the same mass as No. 2270. 

 Ref. Annual Report, xxiv, page 81. 



Meg. This compact, fine-grained graywacke is quite siliceous, almost deserving 

 the name quartzyte. It has pyrite, and is apparently cemented throughout by car- 

 bonate of iron, which, on oxidizing, gives the surface of the rock a rusty color. No 

 section. 



Age. Lower Keewatin(?) N. H. w. 



No. 2272. GRAYWACKE. (Schistose, with chalcopyrite. ) 



Part of the same rock mass as No. 2271, further east. 

 Ref. Annual Report, xxiv, page 81. 



Meg. The rock is more schistose, sericitic, and, while rusty by oxidized pyrite, 

 is also specked with a malachite green color, indicating that the pyrite was copper- 

 bearing. No section. 



Age. Lower Keewatin (?) 



Remark. The copper in this rock may be compared with the metallic copper 

 found in the Lower Keewatin at Tower, No. 2278. N. H. w. 



No. 2273. ARGILLYTE. (Breccia. ) 



On the trail from Moose lake to Wood lake, about the centre of sec. 20, T. C4-9 W., westward from the 

 exposure of conglomeratic jaspilyte. The last and highest ridge before reaching Wood lake. 

 Ref. Annual Report, xxiv, page 82 : Final Report, vol. iv, pages 557-5(>'J. 



Meg. The ridge is composed of a fine, compressed reibnngs breccia of fine 

 graywacke and argillyte, the two rocks being closely folded and broken uniformly 

 into a series of alternating short parts. " On the upper weathered surface where 

 glaciation Has evenly planed the rock off, the two parts recur with an irregular regu- 

 larity, causing the rock to present an aspect of a squeezed conglomerate. But on 



