362 THE GEOLOGY OP MINNESOTA. 



[Schist. 



Meg. The usual jaspilyte of the Vermilion iron range. One of the specimens 

 is gray, another brownish and another red. The last is finely banded with darker 

 bands which contain small magnetite crystals. 



No section. 



Age. Archean (Keewatin). u. s. G. 



No. 431. MICA SCHIST. 



"Rock that forms the first rapids of Pike river; three feet of gray, firm, fine-grained, heavy, crystalline 

 rock, similar to some of the beds of the jaspilyte and slate formation." S. W. % N. W. J4 sec - 3i T. 61-16 W. 

 Ref. Annual Report, ix, page 105; Annual Report, xv, page '211. 



Meg. A hard, fine-grained rock, apparently containing much quartz. Numerous 

 glistening, small cleavage faces of mica are seen throughout the rock. 



Mic. The section shows a rock composed largely of feldspar. This is in grains 

 of considerable size, which have irregular outlines and which are surrounded by a fine- 

 grained mass of similar feldspar with perhaps some quartz. The large grains of 

 feldspar are not very sharply marked off from the smaller ones, but many of inter- 

 mediate sizes occur. The feldspar rarely shows cleavage or twinning and the species 

 was not determined. Scattered through the rock, and lying with their long axes in 

 all directions, are small flakes of Muscovite. These cut through the feldspar. There 

 are also a few minute brownish biotite scales chlorite scales and a little epidote. A 

 peculiar feature of the rock is the presence of large amounts of black dust-like 

 material. 



One section. 



Age. Archean (Keewatin). u. s. G. 



No. 432. BIOTITE SCHIST. 



" In general a gray quartzyte, but varying to a syenitic rock, and to a siliceous slate, and to white quartz, 

 as well as to a tremolitic (?) mica schist, which is dark gray. It exhibits small faults, in which the otherwise 

 parallel and regular strata, or laminations, are jagged or twisted, the west end moving southward about five 

 inches or less. This rock, except in its perpendicular arrangement, and the absence of trap, resembles the gray 

 quartzyte formation of Pigeon point. It is more highly tilted, and generally metamorphic. The beds are nearly 

 perpendicular, but dip to the south." Falls of Pike river; N. W. M S. W. J^ sec. 3, T. 61-16 W. 



Ref. Annual Report, ix, page 105. 



Meg. The hand specimen shows alternations of layers of a hard, dark -gray, 

 siliceous, almost slaty rock and of lighter colored, coarser grained rock, which 

 contains small white feldspars. There are gradations between these two extremes 

 and also very fine laminae, the whole showing a fine example of sedimentary banding. 



Mic. The section, which is small, shows a biotite schist. It is composed essen- 

 tially of a fine-grained aggregate of biotite, quartz and. feldspar. Most of the biotite 

 is cut parallel to the cleavage. There is more quartz present than feldspar, but the 

 two are not easily distinguished, the feldspar being clear and fresh and untwinned. 

 The feldspar shows no cleavage and its species Cannot be determined. The most 



