714 THE GEOLOGY OF MINNESOTA. 



[Greenwarkc. Diabase. Bsterellyte. 



have been named greenstone. This seems to be the prevalent character of the 

 greenstone area about Ogishke Muncie lake. These rocks have not been sheared; 

 indeed, shearing is almost unknown in this district, and is rare in the state, and 

 all original structures as well as original composition are well preserved, as shown 

 by the characters of the rock forming the summit of East Twin mountain (No. 1386). 

 Nos. 1391-1395 represent the broken and sedimentary beds intervening between 

 the Twin peaks and Ogishke Muncie lake, sometimes running in lower ranges and 

 also forming isolated small hills. N. H. w. 



No. 1896. GKEENWACKE. (Regenerated.) 



From the hill directly east of Alpha lake, sec. 29, T. 65-G W. 

 Ref. Annual Report, xvi, pages 100, 124. 



Meg. Uniform, green, rather fine-grained, appearing like a massive rock. 



Mir. This rock does not show the differences of granular structure seen in No. 

 1395, but the grains are of uniform size. They are all small. The most abundant 

 are of hornblende, and invariably show two periods of growth, but there are a few 

 of epidote( ?) indicated by a faintly yellow color and higher double refraction. These 

 are yellowish and short, while the hornblendes are greenish and mostly elongated 

 in section. The fe/i/x/itn- grains are smaller, and indistinct, hiding themselves in the 

 obscurity of the fine groundmass, which last is largely isotropic between the nicols, 

 though plainly containing numerous imperfectly polarizing crystalline elements. 



Several of the hornblendes appear between crossed nicols like enlarged feld- 

 spars, but on making tests in convergent light these give the figure of an optic axis 

 in the field, which fully accounts for their low illumination, and hence for their 

 resemblance to feldspars. One section. 



Age. Archean (Keewatin). 



1-ii'inwk. This rock, which is allied to the green schist of Kekequabic lake, is a 

 difficult one to name. In the field it was taken for a part of the fragmental rocks of 

 the region. Its secondary hornblendic growths are perhaps due to the action of 

 later metamorphic force, intensified by the dike(?) (No. 1397) which cuts it near the 

 lake shore. N. H. w. 



No. 1397. DIABASK. 



Cutting No. 139(5. 



Ref. Annual Report, xvi, pages 100, 124. 



Meg. A medium -grained diabase, with its augite evidently, largely changed to 

 hornblende. Also contains pyrite. No section. 



Ar/e. Archean, probably. u. s. o. 



NO. 1398. ESTEKELLYTE. 



North side of Kt<ke<|uahic lake on tho point on which is the southwest corner of see. "Jit, T. 05-fi W. Same 

 a> No. 1399. 



Ref. Annual Report, xvi, pages 100, 124. 



