828 THE GEOLOGY OF MINNESOTA. 



(Conglomerate. Graywacke. Granite . 



No. 2038. CONGLOMERATE. 



East shore of Oak lake, in Ontario, and about 200 paces north of the portage mentioned under No. 2033. 

 Ref. Annual Report, xxiv, page 20. 



Meg. Coarse, gritty rock, similar to No. 2031, but containing a few sub-rounded 

 quartz pebbles about half an inch in diameter. No section. 



Age. Archean (Upper Keewatin). u. s. G. 



No. 2043. GRAYWACKE. (Slaty.) 



East side of the little bay in sec. 24, T. OC-6, Saganaga lake. 

 Kef. Annual Report, xxiv, page 21. 



Meg. Fine grained, gray, weathering yellowish, in conformable contact with 

 recomposed granite, and interstratified with it, appearing slaty. 



Mic. A fine fragmental slate or graywacke. With a few angular grains of 

 quartz is much of calcite and still more of an ill-defined, dirty-gray substance whose 

 nature it is difficult to determine, but which is a common product of fine trituration 

 of the debris of crystalline rocks, embracing apparently more of the ferromagnesian 

 elements than the lighter colored strata adjacent. In higher power this is some- 

 what resolved into quartz, mica, calcite and apparently some iron oxide, the last giving 

 color to the rock. One section. 



Age. Archean (Upper Keewatin). N. H. w. 



No. 2044. GRANITE. 



Northeastward from the last across the strike ; N. E. J S. W. y sec. 19, T. 66-5. 

 Ref. Annual Report, xxiv, page 21. 



Meg. In a ridge of granite, evidently the source of the debris of Nos. 2032 and 

 2043. 



Mic. The grains all interlock, but the feldspars are all much altered by weath- 

 ering. It is noticeable that this decay is uniform throughout the large crystals, and 

 consists in the formation of myriads of scales of mica and irregular forms or clusters 

 of calcite. This decay thus contrasts with the decay seen in the "old feldspars" seen 

 in the granite of Kekequabic lake. Still there is occasionally a narrow zonal band 

 about some of these feldspars which is less affected by the prevalent decay. One 

 section. 



Age. Archean (granite). N. H. w. 



No. 2045. GRANITE. (Weathered.) 



Same place as the last, but nearer the graywacke. 

 Ref. Annual Report, xxiv, page 22. 



Meg. Granite, which shows the ferromagnesian mineral altered to a straw 

 yellow, laminated nacreous mineral. 



