PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 783 



Quartzyte. Greenstone. Muscovadyte.] 



No. 1779. QUARTZYTE. 



Same place as the last, on the north slope of the same hill. 

 Ref. Annual Report, xxi, page 159. 



Meg. Some of this appears micaceous. Underlies the muscovadyte-gabbro 

 (No. 1778). 



Mic. The quartz is in coarse interlocking grains. It is accompanied by actinolite 

 and Magnetite, and has numerous inclusions. One section. 



Aye. Keewatin (recrystallized jaspilyte), or perhaps Animikie. N. H. w. 



No. 1780. GREENSTONE. (Regenerated.) 



Just across the creek, north from the foregoing, in the eastward extension of the greenstone and gneissic 

 greenstone seen at the northeast corner of Gabemichigania lake. 

 Ref. Annual Report, xxi, pages 148, 149, 159. 



Meg. Greenish gray, massive. 



Mir,. A pyroxene, probably augite, is abundant in this rock, forming ragged 

 crystals that embrace not only magnetite, but also many globular pyroxenes and 

 secondary feldspars, but biotite was later than some of the small globular pyroxenes, 

 and hornblende sometimes replaces them. The rock shows numerous remains of the 

 original old feldspars, now granulitized. It also contains a little hypersthene. One 

 (thick) section. 



Age. Archean (Keewatin). 



Remark. The muscovadyte-gabbro No. 1778, which here immediately overlies 

 the Pewabic quartzyte, is essentially the same as the regenerated greenstone which 

 underlies it. They are both of the muscovadyte type. The nearness of one to the 

 other topographically, and this close petrographic alliance, compel to the assumption 

 that they are the same rock, and that the quartzyte is embraced in that rock. There 

 seems to be here almost a demonstration that the Pewabic quartzyte and its ferru- 

 ginous qualities result from an alteration of masses of jaspilyte in the greenstones 

 of the Keewatin. N. H. w. 



No. 1781. MUSCOVADYTE. ( Granulitic, gaJbbro. ) 



Lies below the same quartzyte. N. E. % sec. 35, T. 65-5, a little east of No. 1780. 

 Ref. Annual Report, xxi, pages 148, 149, 159. 



Meg. When collected this was supposed to be a part of the greenstone of the 

 Archean. 



Mic. But it is a form of thegabbro, constituting the well-known "muscovado 

 rock," which pertains to the " basal " parts of the gabbro. It has essentially the 

 structure of No. 1780, but the pyroxenes have more the color and habit of augite, 

 earlier than the feldspars. There is considerable magnetite in fine grains scattered 

 throughout the slide, some quartz and some biotite and a little uralite and brown 



