PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 525 



Limestone. Flint. Slate.] 



the Huronian in this part of the state, but after passing the valley in which are the 

 calcareous schist and the marble, it is north and south. That the change is some- 

 what sudden is shown by the fact that the beds running north and south are seen to 

 cease abruptly, and to be replaced by the conglomerate in a number of places. The 

 conglomerate in these cases is, so far as seen, rather finer than the average." 



u. s. G. 

 No. 740. LIMESTONE. (Siliceous.) 



Associated with No. 743. 



Ref. Annual Report, x, pages 91, 97; Annual Report, xv, page 371; Annual Report, xvi, page 95; Bulletin 

 vi, page 17. 



.]//. A very fine-grained, gray marble. It has been considerably fissured and 

 cemented, largely by quartz, and from the hardness of the rock one would think that 

 fine-grained quartz was disseminated all through it. 



Mic. The main part of the rock is composed of very fine-grained, gray calclte 

 with a little quartz also in minute grains. Larger grains of calcite are, however, also 

 present. The rock appears to have been crushed, and the fine grain of the calcite is 

 probably due to the crushing. There are also numerous fissures in the section. The 

 smaller fissures are filled in with calcite, which is more transparent than that of the 

 main mass of the rock, and the larger fissures are filled by both calcite and quartz. 



Two sections examined. 



Age. Keewatin. u. s. a. 



No. 747. FLINT. 



S. W. % S. E. y sec. 26, T. 65-6 W.; east shore of Ogishke Muncie lake. 

 Ref. Annual Report, x, pages 92, 94. 



Meg. A black, very hard, aphanitic rock. 



Mic. The most noticeable feature of the section is the presence of numerous, 

 small, irregularly outlined spots which are of darker color than the rest of the rock. 

 These spots at times show a slight absorption, and under crossed nicols they polarized 

 like carbonate. They are probably largely sirferife. Aside from these spots the sec- 

 tion is made up almost entirely of cryptocrystalline silica, with considerable opaque 

 dust-like material. 



One section examined. 



Aye. Keewatin. u. s. G. 



No. 748. SLATE. 



Portage between Ogishke Muncie and Dyke lakes; N. W. J4 S. W. J4 sec. 27, T. 63 6 W. 

 Annual Report, x, page 93. 



Mc(j. A fine-grained, slaty rock, greenish-gray to black in color. One side 

 shows a black, apparently carbonaceous layer. With cold hydrochloric acid the rock 

 effervesces rather freely. 



