PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 683 



Jaspilyte. Sericite Bchist. Porphyrel.] 



with hematite or limonite scales and by darker concentric layers of the same, presenting 

 pisolitic structure. The concentric structure pertains, however, only to the borders 

 of these grains, their interior portions being amorphous, and supposed to have been 

 originally of ylaucot/ite. One section. 



Age. Animikie. lying below the limestone No. 1289 at least further north. 



N. H. w. 

 No. 1295. JASPILYTE. 



Same place as the last ; portion of the same mass. 



Ref. Annual Report, xvi, pages 69, 120 ; Bulletin vi, pages 115, 122. 



Meg. Red and gray, flinty. 



Mir. There are no round masses of the changed glauconite in this portion of 

 the rock, but while the mass in general consists of the same interlocking, secondary 

 quartz grains, the iron films, instead of being concretionary, are in parallel fine films 

 nearly straight, lying in the body of the quartzitic mass. These give color to the rock. 

 As these are wanting, and as the quartz becomes finer, so the rock approaches flint. 

 Compare No. 1277. Two sections. 



Age. Animikie. N. H. w. 



No. 1296. SERICITE SCHIST. 



On a traverse made north from Gunflint lake, about half a mile west of the east end of the lake. 

 Kef. Annual Report, xvi, pages 69, 120. 



Meg. A h'ne-grained, hard, siliceous, gray, roughly schistose rock, with minute 

 scales of a mineral like sericite. No section. 



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



Nq. 1297. PORPHYREL. (Schistose. ) 



On the same line, north from Gunflint lake, in Canada, as Nos. 1294 and 1295. 

 Ref. Annual Report, xvi, pages 69, 120. 



Meg. Porphyritic with feldspars. Compare Nos. 1279, 1283 and 311. A fine- 

 grained, siliceous rock, gray or greenish gray, with some pyrite. 



Mic. Large patches of adinolite are perhaps the most conspicuous element in 

 this rock. They are light green in natural light, but show a slightly darker green 

 when the polarizer only is used, and the fibres are brought into parallelism with its 

 principal section. Smaller particles and single fibres are scattered through the slide. 



Quartz is the next in importance. It is distributed everywhere in fine sub- 

 angular, glassy, clear grains, forming the general matrix. These grains are generally 

 not in contact, but are separated by another finer matrix which becomes visible on 

 lowering the condenser in natural light, but which is translucent in general, and 

 polarizes aggregately between crossed nicols, apparently a kind of kaolin. But these 

 quartzes are sometimes larger and in contact. They then have more irregular shapes 



