PETROGRAPHIO GEOLOGY AND DESCRIPTIONS. 507 



Qraywacke.] 



Meg. A tine-grained, compact black rock, appearing like a diabase. 



Mir. The section shows feldspar, green hornblende, magnetite, Inotite, chlorite, and 

 possibly a few small grains of quartz. The feldspar is usually in elongated grains, 

 and is, in large part at least, plagioclase apparently near innfeninc. The hornblende 

 and magnetite are frequently in elongated grains, and sometimes there is an indis- 

 tinct radial arrangement of these grains. 



One section examined. 



Aye. Cabotian. 



h'fiiid //, This rock represents the tiner grained lower portion of the diabase 

 sill, of which No. 709 represents the main part. It is impossible to tell whether No. 

 710 was originally holocrystalline, and thus whether the secondary minerals may 

 represent original augite or original unindividualized matter. u. s. G. 



No. 711. GUAYWACKE. (Mate.) 



Nos. 711 and 712 make up the lower part of the hill in which Nos. 700 and 710 occur. There is 100 to 125 

 feet in thickness of Nos. 711 and 712; thoy are slaty, and dip towards the south at angles of 10 to 15. About 

 nine-tenths of this slaty rock is made up of No. 711. 



Ref. Annual Report, x, page 84. 



Mi'<j. A very fine-grained graywacke slate, showing small glistening Makes of 

 of some mineral with a marked cleavage. 



Mir. The section shows a tine-grained slate, composed of i/inuiz, possibly some 

 feltlxi><ir, Itiotite, intixcor.ite chlorite, magnetite and pyrite. The biotite is quite abundant. 

 There are a few irregular shaped areas of some transparent mineral which is in 

 much larger grains than the other constituents of this rock. This mineral is 

 evidently the same as that mentioned so abundant in No. 712. 



One section examined. 



Aye. Animikie. 



No. 712. GRAYWACKE. (SMe.) 



- locality as No. 709. See under No. 711. 

 Ref. Annual Report, x, page 84. 



MCI/. A tine-grained, slaty rock, in general resembling No. 711. 



Mir. The most noticeable feature of the section under a low power, or when 

 examined with a hand lens, is the apparent sponge-like texture of the rock, there 

 being lighter areas enclosed in a general background of darker color. The section 

 shows a banding due to the abundance of the iron ores in certain lines. The dark 

 background of the section consists of a very fine-grained aggregate of </itini;, possibly 

 SOaa.6 feldspar, hiotite in abundance, chlorite, musconite, in/rite in abundance, magnetite 

 and hematite. These minerals, except the quartz, are also scattered through the 

 lighter areas in the section, but not in large amount, the dark color of the background 

 being due to the great abundance of biotite and the iron ores. 



