PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 695 



Greenstone. Peridotyte.] 



No. 1334. GREENSTONE. (Muscovadyte.) 



Most southerly exposed part of the same greenstone as No. 1333. In a ridge thirty rods south of Nos. 

 1330-1332, but from its most southerly exposed portion. 



Ref. Annual Report, xvi, pages 83, 84, 121 ; Annual Report, xix, pages 195-197, 199-203. 



Meg. Greenstone. 



Mic. Pyroxene (auyite) in globular and angular grains, and in ragged masses, 

 with plagioclase and a little magnetite. The feldspars are crowded with inclusions. 

 Leucoxene is common in rather dark grains. One section. 



Age. Archean (Keewatin metamorphosed). 



Remark. This rock in its internal structure illustrates the familiar fact that 

 minerals in incipiency under metamorphism assume globular forms at first. These 

 augitic grains are identical with those seen in the pyroxenic gneisses in the long point 

 (Muscovado point) at the northeastern side of Gabemichigama lake, and at other 

 places mentioned, and they are in all cases to be attributed to the general metamor- 

 phosing effect of the gabbro revolution on the clastic greenstones of the Archean. 

 Mr. Bayley argued that this rock is degenerated or crushed gabbro (Nineteenth 

 Annual Report, pages 196, 197). He apprehended its petrographic alliance with the 

 normal gabbro, but put it at the wrong end of the series of change. It is at the 

 incipiency of gabbro rather than at its degeneracy. It is at its cradle rather than at 

 its grave. It was a clastic greenstone originally. It is now a metamorphic rock. 

 The normal gabbro occurs but few rods south of this rock. N. H. w. 



No. 1335. GREENSTONE. ( Muscovadyte. ) 



Rock of the hill north of Chub (Akeley) lake. 



Ref. Annual Report, xvi, pages 83-85, 87, 95, 98, 121 ; Annual Report, xix, pages 195-197, 199-201, 203. 



Meg. A rather indefinite, greenish rock. 



Mic. Hornblende and plagioclase feldspar, in imperfect, fine, granular associ- 

 ation, compose this rock. It has also a globular pyroxene (probably diopside or 

 incipient augite] rather thickly scattered throughout the slide. This is in globular 

 grains and in groupings of grains and frequently small globular pyroxenes are 

 enclosed in the larger. With a little biotite that composes the rock. One section. 



Age. Archean (Keewatin). 



Remark. It is reasonable to assume that this rock was also originally a basic 

 clastic of the greenstone kind. It approaches muscovadyte in its present condition, 

 and as Bayley states might be styled a granulitic gabbro. N. H. w. 



No. 1336. PERIDOTYTE (with fayalite) . 



From an excavation at Chub (Akeley) lake, for ore. This lies on the greenstone No. 1335, dipping south- 

 ward ujider Chub lake. It is closely associated with the iron ore, and is, indeed, a part of the ore of the locality, 

 varying to quartzyte. 



Ref. Annual Report, xvi, pages 83, 84 ; Annual Report, xix, pages 195, 197, 198. 201, 203, 204. 



