346 THE GEOLOGY OF MINNESOTA. 



[Jaspilyte. Arkose. 



Stuntz conglomerate, sections of the matrix of which have been called "sheared 

 quartz " porphyry, causes us to hesitate about stating positively the nature of the 

 rock (No. 387). See under No. 874, and under the description of the Stuntz conglom- 

 erate in vol. iv, pages 526-538. u. s. G. 



No. 388. JASPILYTE. (Grny.) 



Vermilion lake; perhaps near the centre of the E. % sec. 20, T. 62-15 W.* 

 Ref. Annual Report, is, page 97. 



Meg. Fine-grained, gray, cherty rock. 



Mir. The section shows fine, angular grains of quartz, with a few rhombs of 

 carbonate of iron. The latter are idiomorphic and perfect as crystals (or nearly 

 perfect), but the former are crowded upon each other. In one section the siderites 

 are somewhat clouded by included magnetite, and quite frequently they embrace at 

 their centres a powder of magnetite, which is also distributed in clusters elsewhere, 

 giving the section a spotted appearance. It is probable that this magnetite antedates 

 the siderite, only serving as nuclei on which the carbonate grew, while the limonite 

 is seen to be a result, so far as it exists, of alteration from the carbonate, the crystals 

 of which are stained by it. Two sections. 



Age. Archean (Lower Keewatin). 



Remark. The distribution of this magnetite powder in the individual quartzes 

 causes the rock to resemble taconyte. N. H. w. 



No. 389. ARKOSE. 



Vermilion lake; S. W. % S. W. J sec. 20, T. 62-15 W. 

 Ref. Annual Report, ix, pages 97, 98. 



Meg. Gray, compact, coarsely schistose, none of the minerals being well 

 characterized. No quartz is distinguishable under the hand glass, but fine glittering 

 surfaces are visible which are apparently of some mica. The rock has a vague and 

 indefinable aspect, the coarsest grains, which are apparently feldspar and have a 

 diameter of about one millimeter, fading out into the surrounding matrix. The rock 



i 



is evidently of fragmental origin, as indicated by the perfect stratification described 

 by the field notes. 



Mic. The section consists essentially of feldspar (plagiodase), a little quartz, 

 much isotropic chloritic substance, some epidote, muscovite, and a reddish-yellow stain 

 which probably is iron oxide, and calcite. 



The feldspar is sometimes distinctly twinned, and other crystals are destitute 

 of striations. The grains are all much altered, and are specked with flakes of 

 muscovite, which also is scattered irregularly through the finer grains. Two sections. 



Age. Upper Keewatin. 



'When these specimens were collected (18781, the United States land survey had not yet been extended over these localities 

 In making assignments of these localities in the tcrmsof the "towns" and "ranges" of that survey a little allowance must be made 

 for possible error as to the exact locations of the points at which the specimens were obtained. 



