556 THE GEOLOGY OP MINNESOTA. 



[Apobsidian. Aporhyolyte. Anorthosyte. 



No. 812. APOBSIDIAN. 



Two miles west of the palisades, north shore of lake Superior; S. E. J4 sec - 32, T. 5C-7 W. 

 Ref. Annual Report, x, page HO. 



Meg. A very fine-grained, reddish-gray, homogeneous rock, except for a few 

 small areas, which appear to be feldspars, and some linings which are brought out by 

 weathering. These linings are probably due to some flowage phenomena in the 

 original rock. 



Mic. The section is composed essentially of fine-grained quartz and frltlxpar. 

 The latter is much altered and the former exists in small, irregularly outlined, 

 poikilitic areas. This rock is undoubtedly a devitrified glass. There are throughout 



V 



the slide specks of iron ore and of a gray opaque substance. 



Age. Cabotian. u. s. G. 



No. 813. APORHYOLYTE. 



Great Palisades, north shore of lake Superior; sec. 22, T. 56-7 W. 

 Ref. Annual Report, x, page 110. 



Meg. This rock is almost identical with No. 140(7). 



Two sections. 



Age. Cabotian. u. s. G. 



No. 814. ANORTHOSYTE. 



Two and a half or three miles east of Beaver bay, north shore of lake Superior. Compare No. 694. 



"There is one place two and a half or three miles east of Beaver bay, where the 'feldspar rock' is bedded, 

 and dips easterly in all respects like the usual trap of the shore. It here shows also a confused mixture with the 

 trap, in which, in other places, it seems to be (and is) embraced as isolated masses, as at Splitrock point. This 

 bedded condition is very evident in coming from the northeast, as the conspicuous surface slopes in that direc- 

 tion. Narrow dikes of fine-grained, gray doleryte cut the feldspar rock. One dike is six inches wide and one is 

 about nine. They are about parallel, twenty five feet apart, and run east and west by compass. The feldspar 

 here is very coarsely crystalline, and is represented by No. 810. The alternate beds consist of bands of coarse 

 crystals succeeded by layers of fine crystals, in which are also numerous grains of a more rapidly disintegrating 

 mineral which, by becoming disseminated, stains the whole of a green color. This disintegrating mineral seems 

 to take the place of the augite seen in the gabbro; therefore the ' bedding ' is an alternation of gray, coarse feld- 

 spar with green, decaying gabbro. No. 814 represents the feldspar stained iritli !/' i/n-<-n iri'nthi-i-i IKJ nilui-nil. 

 The bands of color are from three to six inches, fading into the uncolored, clear feldspar above and below. 

 About twenty feet of this bedded feldspar can be seen here." [N. H. w.] 



Ref. Annual Report, x, pages 80, 110, 111, 115; Bulletin ii, page 95; Bulletin vi, pages 12G, 421; volume iv, 

 page 302. 



Meg. A rock composed of coarse-grained, greenish-gray plagioclase and a much 

 smaller amount of a soft black mineral, probably serpentine. 



Mic. The section shows a few large grains of plagioclase abundantly twinned 

 according to the albite law, and with a few pericline twinnings. There is a small 

 amount of greenish and brownish (chlorite and serpentine) alteration products. A 

 cleavage chip of the feldspar parallel to 001 gave an extinction angle of 30, and one 

 parallel to 010 gave 33, indicating bytoirnite. 



One thick section. 



Age. Cabotian. u. s. G. 



