784 THE GEOLOGY OP MINNESOTA. 



[Quartzyte. Magnetite. Muscovadyte. 



hornblende. There are visible none of the remains of any old feldspars, and in that 

 respect, as well as in the manner of the pyroxenes, this muscovadyte is different from 

 the less regenerated greenstones. One section. 



Age. Cabotian (regenerated Keewatin). 



Remark. In the annual reports there was some confusion in the use of the 

 term muscovadyte, and an effort was made in the Twenty-first Annual Report, 

 (pages 143-152) to define it more exactly and to assign it to a phase of the gabbro, 

 supposed to be due to shattering of the grains about the periphery of the gabbro 

 mass. The name is based wholly on the miueralogic structure and the prevalent 

 color. 



It has since appeared, however, both in field examination and in the micro- 

 scopical study, that the muscovadyte is altered both to the gabbro and to the green- 

 stone of the Keewatin, being an intermediate stage in the transformation of the 

 great Keewatin greenstone mass into the great irruptive gabbro mass. Compare the 

 description of rock No. 2197; also the discussion in Part I. N. H. w. 



No. 1782. QUARTZYTE. 



Top of the ridge at the same locality as No. 1781. 

 Ref. Annual Report, xxi, page 159. 



Meg. Vitreous quartzyte, varying from coarse to fine grained. Similar to No. 

 1779. No section. 



Age. Pewabic. u. s. o. 



No. 1783. MAGNETITE. 



From a cliff at the southeast end of Paulson lake, S. E. J S. E. % sec. 25, T. 66-5 W. 

 Kef. Annual Report, xxi, page 159. 



Meg. Bather fine-grained, crystalline magnetite. No section. 



Age. Pewabic. u. s. G. 



No. 1784. MUSCOVADYTE. 



North side of Muscovado lake. 



Ref. Annual Report, xxi, pages 150, 160 ; Annual Report, xxiii, pages 212, 214. 



Meg. Heavily jointed, nearly horizontal, slides in sheets into the lake toward 

 the southeast, the sheets being from one-half inch to six inches thick. Prevails 

 about the shores of Muscovado lake, and on the shores of the north half of the 

 Bashitanequeb lake, forming hills north of the latter. 



M ic. It has the elements of a gabbro, the augite being earlier or cotemporary with 

 the feldspar, with considerable magnetite and hypersthene; no quartz, the grains being 

 of even size, all rather fine and affecting a roundish habit. Very frequently the 

 augites and hypersthene are embraced wholly within the feldspars. Two sections. 



Age. Cabotian (altered Keewatin). 



