304 THE GEOLOGY OP MINNESOTA. 



[Diabase. Gabbro. Slate. 



Meg. A fine-grained, rather light greenish, gray quartzyte. 



Mic. The section is composed of rounded and subangular quartz grains, some- 

 times showing secondary enlargements, and a few feldspar grains in an abundant 

 cement, which is composed largely of chlorite, and quartz and feldspar in minute 

 grains. 



One thick section. 



Aye. Animikie. (Grand Portage gray wacke.) u. s. G. 



No. 296. DIABASE (with olivine). 



From a dike near the brink of Partridge falls in Pigeon river. The axis of a hill range, supposed to be 

 the same as that from which was derived No. 294. This dike runs W. 5 N.; at least 110 paces wide. 

 Compare No. 774 (W.), Annual Report, xvi, page 291. 

 Ref. Annual Report, ix, pages 73, 74; Bulletin ii, page 106. 



Meg. Apparently an olivine diabase of a dark color, and of uniform grain. 

 Mic. This rock has the same characters as No. 293. The rock is fresh, and the 

 olivines even are well preserved. 

 One section. 



Age. Cabotian. N. H. w. 



No. 297. GABBRO (with olivine). 



English rapids (upper end), near the centre of theN. J sec. 21, T. 64-4 E. 



Ref. Annual Report, ix, page 74; Annual Report, x, page 140; Bulletin ii, page 106; American Association 

 for the Advancement of Science, vol. xxx, page 163. 



This rock, which also comes from a dike, again illustrates these great dikes, 

 which cut so numerously the Animikie slates of the region. The augite is both 

 ophitic and idiomorphic, and the whole rock is fresh, making a beautiful microscopic 

 slide. In one of the ophitic augites the same character is observed as seen in No. 

 291, i. e., the optic angle round n s is abnormally small, in this case being about 20. 

 Two sections. 



Age. Cabotian. N. H. w. 



No. 298. DIABASE (luith olivine). 



Top of the hill on the east of the portage trail, at the foot of South Fowl lake. This lies on the slates, and 

 was probably injected as a sill between the slates originally, the overlying slates having been destroyed. It has 

 a perpendicular basaltic structure. 



Ref. Annual Report, ix, pages 74, 75; Bulletin ii, page 108. 



Mic. This rock is undistinguishable from Nos. 293, 296 and 297, except that 

 the minerals are all more decayed. Macroscopically, much pyrite is apparent in 

 this rock. 



Two sections. 



Age. Cabotian. N. H. w. 



No. 299. SLATE. 



" Fragment of the slate from below No. 298; ten feet below the contact." Same locality as No. 298. 

 Ref. Annual Report, ix, page 75; Annual Report, xvi, page 72. 



