610 THE GEOLOGY OP MINNESOTA. 



[Greenstone. Cumniingtonite schist. Quartz. 



No. 949. "GREENSTONE." 



See under No. 948. 



Ref. Annual Report, xv, pages 329, 390. 



Mey. A tine-grained, soft, much decayed greenstone. 



Mic. The section is a poor one. It shows irregular grains of feldspar and 

 tjtuniz, also some hornblende and much chloritic indistinct secondary material. The 

 feldspar is much altered, zoisite and kaolinite having been developed in the alteration, 

 and some of it still shows albite twinning lamellae. 



One section. 



Age. Keewatin. u. s. G. 



NO. 950. CUMMINGTONITE SCHIST. 



"At the lower end of the rapids which are formed where White Iron lake descends to Garden lake, N. E. 

 % sec. 32, T. 63-11, are two short, small tunnels, running in opposite directions, into a siliceous schist or bedded 

 quartzyte, which disturbs the compass needle by magnetic attraction. It dips N. N. E. 80 to 85. It is some- 

 what brecciated, and recemented by chemical silica and pyrites. In some places this bedded quartzyte is black, 

 and in others blue, sonorous and brittle, recalling the Aniniikie quartzytes. It is represented by No. 950. The 

 quartz in which the tunnels were excavated is represented by No. 951. This locality is known locally as Silver 

 City, so named by the proprietor of the tunneling." 



Ref. Annual Report, xv, pages 329, 390; Annual Report, xvii, pages 194, 208; Bulletin vi, pages 8, 421. 



Meg. A fine-grained, hard, gray, siliceous schist. 



Mic. The rock is composed of three minerals, quartz, cummingtonite and magne- 

 tite. The main part of the rock is of quartz, and the other minerals vary consid- 

 erably in amount. The quartz is in interlocking grains of nearly uniform size. The 

 cummingtonite is in small flakes scattered through the rock, the elongation being 

 usually in a common direction. This mineral at times shows twinning lamellae 

 parallel with the elongation and the cleavage, and an extinction angle as high as 

 15. These characters agree with grilnerite, but on account of the double refraction 

 of this mineral, which is approximately .02, it is referred to cummingtonite rather 

 than to grunerite, whose double refraction is much stronger (.056). The magnetite 

 is scattered through the rock and is often included in the quartz; the magnetite is 

 in grains and crystals (octahedrons) of varying size. 



Three sections. 



Age. Keewatin. u. s. G. 



No. 951. QUARTZ. 



Same locality as No. 950. 



Ref. Annual Report, xv, pages 329, 390; Bulletin vi, pages 8, 421. 



Meg. Gray, vitreous, rusty-weathering, vein quartz. 



Mic. The section shows quartz grains of various sizes interlocking by very 

 irregular sutures. Considerable of a dark, earthy material is scattered through the 

 rock in small masses. One section. 



Age. Vein in Keewatin rocks. u. s . G. 



