PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 521 



Tuff. Slate.] 



M/e. M. E. Wadsworth's description of this rock is as follows:* 



"A gray, fragmental, much indurated rock, containing quartz grains and many 

 small pebbles. It resembles a consolidated sandstone. This belongs more properly 

 with the schists and sandstones, but is described here on account of its connection 

 with No. 73'J. The section is apparently a transition specimen between one composed 

 of basaltic material and one composed of granitic and felsitic (quartz-porphyry) debris. 

 The major part of the section is made up of quartz and feldspar fragments, with 

 rounded masses of felsyte (quartz-porphyry) and some fragments of argillyte and 

 melaphyr. I' i/ rite is common. The same alterations have taken place in melaphyr 

 and feldspar as before described, while the felsyte groundmass isdiversified into a con- 

 fused granular mixture of quartz, feldspar, micaceous and chlorite scales. The quartz 

 and feldspar fragments are apparently from a granite." 



One section examined. 



Ar/e. Ogishke conglomerate, at the base of the Upper Keewatin. n. s. G. 



No. 739. TUFF. ( VolmiiM. ) 



Ogishke Munoie lake; probably in N. W. 14 sec. 24, T. G5-6 W. 

 Ref. Annual Report, x, page 90: Bulletin ii, pages 122, 123. 



Mi'!/. "A dark, greenish, compact, feldspathic groundmass, with greenish mate- 

 rial scattered irregularly through this groundmass. A few lath-shaped feldspars also 

 occur in the groundmass." 



Mic. M. E. Wadsworth's description of this section is as follows :f 



" The section is composed of rounded and irregular rock fragments with their 

 cementing debris. So far as the character of these fragments can now be ascertained, 

 they appear to be basaltic (melaphyr) with some probably more acidic ones. The 

 />//ro.rene has been entirely altered to chlorite, and the feldspar largely to chlorite and 

 colorless micaceous scales, but the triclinic character of many of the crystals is still 

 distinct in polarized light. Much pyrite in grains is to be seen, while the ground- 

 mass is changed to chlorite and colorless micaceous scales with quartz." 



There is also a considerable amount of a carbonate, which shows at times a 

 quite noticeable absorption xuh-ritc, probably. 



One section examined. 



Age. Keewatin. u. s. G. 



No. 740. SLATE. 



North shore of Ogishke Muncie lake; probably in N. W % sec;. 24, T. 65-0 W. 

 Kef. Annual Report, x, pages 91, 93, 94. 



Meg. A fine-grained, dark-gray, clay slate. 



*Jtulleliitii,pi>. I-':', IS. 

 ^Bulletin it, p. 122. 



