PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 555 



Shale. Anorthosyte. Granite.] 



No. 809. SHALE. (Red.) 



Boyle's quarry, on the railroad above Pond du Lac. 



Ref. Annual Report, x, page 109; Annual Report, xiii, pages 100, 103 (No. 166). 



Meg. Soft, fine-grained, red shale, with a few small, gray, circular areas, which, 

 aside from the color, do not appear particularly different from the rest of the rock. 



A chemical analysis of this rock gave the following results: 



SiO 2 48.92 



A1 2 O 3 18.45 



Fe 2 O 3 16.88 

 FeO 0.57 



CaO 0.70 



MgO 3.68 



Na 2 O 0.48 



K 2 1.32 



H,O - 7.14 



Total 98.14 



No section. 



Age. Upper Cambrian. u. s. G. 



No. 810. ANORTHOSYTE. 



Two and a half or three miles below Beaver bay. 



Ref. Annual Report, x, pages 109, 110; Bulletin vi, pages 126, 421. 



Meg. An extremely coarse-grained mass of plagioclase feldspar, frequently 

 showing albite twinning. Compare No. 814, which is coarsely laminated as a rock. 



Mic, The section, except for small impurities or products of alteration, is of 

 plagioclase, commonly showing broad albite twinning lamellae. There are some 

 small earthy areas which may represent the alteration products of augite inclusions. 

 Kaolin and chlorite are present as alteration products, also a little of a brownish 

 mineral in cracks. Cleavage chips of the feldspar parallel to 001 gave extinction 

 angles of 22 and 23, and those parallel to 010 gave angles of 30 and 32. These 

 angles indicate Injtownite. 



One section. 



Age. Cabotian. u. s. G. 



No. 811. GRANITE. 



" From the large red -granite island, three or four miles below Beaver bay, which is arched on the lake- 

 ward side." 



Ref. Annual Report, x, page 110. 



Meg. A medium-grained, dark-red granite, composed of red feldspar, quartz 

 and some dark material. 



Mic. The section shows one of the usual " red rocks." The minerals are feld- 

 fsptn; altered and much reddened, quartz, hematite and magnetite. The quartz and 

 feldspar in places are intergrown in a pegmatitic manner. 



One section. 



Age. Cabotian. u. s. G. 



