896 THE GEOLOGY OP MINNESOTA. 



[Granite. 



No. 523G. GRANITE. 



North shore of Snowbank lake, N. W. J S. W. % sec. 29, T. 64-8 W. 

 Ref. Annual Report, xx, pages 66, 103 ; Annual Report, xxii, page 156. 



A medium-grained gray granite, with small yellow stains. 



Mic. Dr. A. H. Elftman's description of this rock is as follows (Twenty-second 

 Annual Report, page 156): " No. 523G from the N. W. i of S. W. i sec. 29, T. 64-3, 

 is a medium-grained hornblende granite of a light-gray color. Examined in thin 

 section, this rock shows the usual composition of the hornblende granite in this 

 locality. The feldspars are considerably altered, quartz occurs only in small grains, 

 and the hornblende is highly pleochroic in green and brown. Sphene is the oldest 

 mineral. Magnetite is largely secondary. Limonite, an alteration product, stains the 

 rock yellow. Combined with the kaolin of the feldspar this produces a yellow 

 powder which is easily removed from the rock and leaves cavities. In the hand 

 specimen this peculiar yellow stain is very noticeable." Two sections. 



Age. Archean. u. s. G. 



No. 524G. GRANITE. (Augitic.) 



East shore of Boot island, Snowbank lake. This island is the one crossed by the line between ranges 8 

 and 9 west. 



Ref. Annual Report, xx, pages 67, 103 ; Annual Report, xxii, page 157. 



Meg. A medium-grained, dark-gray granite, in which the ferromagnesian 

 minerals are abundant. 



Mic. Dr. A. H. Elftman's description of this rock is as follows (Twenty-second 

 Annual Report, page 157) : " No. 524G, from the east shore of the large island (Boot 

 island) on the range line between T. 64-8 and T. 64-9, is a coarse augite granite. In 

 general the rock is the sarneas No. 271E,* differing only in the character of the augite, 

 which in this section is fresh, shows no signs of alteration, is not pleochroic, 

 extinguishes at 45 and has a deep green color." Biotite is common. Three sections. 



Age. Archean. u. s. o. 



No. 551G. GRANITE. (Augitic.) 



From a little promontory on the south shore of Kekequabic lake, S. W. % S. W. J^ sec. 3, T. 64-7 W. 

 Ref. Annual Report, xx, pages 71, 104 ; Annual Report, xxi, pages 39-50. (This rock is a good representa- 

 tive of the normal phase of the granite here described.) 



Meg. A fine-grained, pinkish-gray granite composed of pinkish feldspar, quartz 

 and small grains of augite. Sub-porphyritic feldspars are common. . 



Mic. Under the microscope the sub-porphyritic feldspars are not so noticeable, 

 except for their size, as in the hand specimen. All the feldspar has a tendency to 

 an idiomorphic form, and all is somewhat clouded by alteration. It is frequently 

 polysynthetically twinned and sometimes, especially in the larger crystals, is zoned. 

 On separating the powder of this rock by means of Thoulet's solution, the larger 



*For the description of No. 271E see foot-note under No. 522O. 



