726 THE GEOLOGY OP MINNESOTA. 



[Granite. Grayw.ic-kc. 



Mi<-. In the usual fine groundmass, largely of actinolitic and feldspathic 

 materials, are J/onililcndes which, having the form of the augite in the porphyry, are 

 evidently derived from that mineral by uralization. The rock contains no evident 

 old feldspars. The hornblendes have secondary growths. One section. 



Aije. Arcliean (Keewatin). N. H. w. 



NO. 1427. (IKANITK. 



On the portage from Spoon lake northward. 

 Ref. Annual Report, xvi, page 125. 



Meg. A drift piece showing the red rock cutting a biotitic gneiss. Must h;i\r 

 come from some place further north or northeast. 



Mic. The nature of the rock shows that it belongs with the Kekequabic lake 

 series of granites. The supposed " vein " consists of a belt across the slide in which 

 biotite is wanting, making it appear lighter colored and perhaps causing a redness 

 on weathering. The whole rock is coarsely crystalline. Indeed the old feldspars 

 are regenerated by new growths, and in many instances the clear new growths make 

 up their principal portion. They embrace ophitically new hornblendes, /^/mn//r.s 

 and biotite, while the old ones are free (or almost free) from them, are much 

 twinned, clouded and eaten into by the fresh quartz-feldspar granulitic (and granitic) 

 groundmass. The old feldspars are abundant in the so-called vein, and the fresh 

 growths are in the rock on either side. One section. 



Age. Archean (Keewatin). 



Remark. This is a rock, whatever its source, which must, however, be near its 

 present place, which shows how the old feldspars and hornblendes, and the old 

 micro-granulitic matrix are converted into a coarser, fresh, firm granite. What 

 could have caused this but igneous contact? It indicates that further toward the 

 northeast is probably an outcrop of such granite in the midst of the green schists, and 

 if it has been correctly explained, there should be evidence of some sort of gabbro 

 activity in the vicinity. N. H. w. 



No. 1428. GRAYWACKE. 



Southeast shore of Knife lake ; the point which is near the centre of the east side of N. E. J^ sec. 28, 

 T. (iTi-7 W. 



Ref. Annual Report, xvi, pages 109, 125 ; Annual Report, xvii, pages 200, 206. 



Meg. Siliceous slate. 



Mic. A fragmental rock, of quartz and old feldspars (the coarsest elements), 

 -ite and a fine matrix of quartz, feldspar and leucoxenc. One section. 

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



No. 1436. GRANITE. 



S.-c:. 10, T. 64-10, Bassimenan (Basswood) lake. 



Ref. Annual Report, xvi, pages 110, 126 ; Annual Report, xvii, pages 200, 200. 



