578 THE GEOLOGY OF MINNESOTA. 



[Quartzyte. Jaspilyte. 



concentration is more noticeable when the slide is examined with a low power than 

 with a high one. The bands of magnetite, mentioned in the description of the hand 

 sample, are seen to be sponge-like bands of this mineral holding some quartz and a 

 little hematite. (See the description of No. 867.) 



Three sections. 



Age. Lower Keewatin. u. s. G. 



No. 866A. QUARTZYTE. (Ferruginous.} 



From nodules embraced in No. 866. - 



Kef. Annual Report, xv, pages 265, 266, 386; Annual Report, xvi, page 65. 



A medium-grained rock, bright red, dull red and gray black in color, the 

 latter color being due to a considerable amount of specular hematite. 



Mic. The section shows a rock composed of interlocking grains of quartz 

 which is more or less completely saturated with other material. This material can 

 be divided into three principal groups: (1) Blood-red hematite scales and grains; 

 (2) Magnetite grains, not very abundant; and (3) A yellowish to brownish, some- 

 what earthy substance. The last is very abundant and exists in irregular areas and 

 also collected into arborescent forms, which at times assume the aspect of branching 

 sea weeds. This substance seems to have no effect on polarized light. Just what it 

 is, is not clear. 



One thick section. 



Age. Lower Keewatin. 



Remark. The bright red parts of the hand specimen resemble No. 2279. 



u. s. G. 



No. 866B. JASPILYTE. 



Near the same place as No. 866. 



Ref. Annual Report, xv, pages 265, 266, 386; Annual Report, xviii, page 34. 



Meg. A light-gray to dark-gray, finely laminated jaspilyte. Some porous bands 

 of limonite are present. 



Mic. The section shows the usual mosaic of quartz grains. Thickly scattered 

 through the slide is black, opaque, dust-like material. This is probably in large part 

 nidi/netite, as the powdered rock yields a number of particles to the magnet. There 

 is also considerable limonite present. 



One section. 



Age. Lower Keewatin. u. s. G. 



No. 867. JASPILYTE. 



Near the same place as No. 866. 



Ref. Annual Report, xv, pages 265, 266, 386; Bulletin ii, pages 10, 72-79, 81, 421, plate VII, and figure 1 

 of plate VIII. 



