388 THE GEOLOGY OP MINNESOTA. 



[Graywaeke. 



Mic. All the characters mentioned under No. 502 appear in this rock except 

 hornblende and epidote, and in addition one good sized and two smaller microscopic 

 crystals of rutile are present. In the larger crystal the plane of the larger section 

 happens to be so nearly perpendicular to the optic axis as to show unmistakably the 

 uniaxial interference figure in convergent light; the grain also exhibits the four, 

 intersecting cleavages in two systems standing at 45 with each other, each system 

 having its own intersection at 90. Biotite is also scantily generated in this rock 

 and abundance of apatite. Chlorite stains some of the feldspars. 



One section. 



Age. Cabotian dike in the Keewatin(?) 



Remark. The above rutile grains are undoubtedly original. They are not in 

 association with any possible alteration products from ilmenite. The largest grains 

 are themselves somewhat altered about their margins, and while they are idiomor- 

 phic their outlines still are blunted. N. H. w. 



No. 504. GRAYWACKE. 



At two miles and a half north of Carlton, on the railroad. 



Ref. Annual Report, x, pages 28, 29; Annual Report, xviii, page 47. 



Mey. Contains black pebbly masses of what appears to be argillyte. These are 

 somewhat rounded, often half an inch in larger dimension, and occasionally two inches 

 long. They are covered with a black, shining and slippery coating, apparently 

 slickensided. 



Mic. Quartz, feldspar (microcline, orthoclase, plagioclase) muscovite, chlorite, 

 calcite, ziron(?), with more or less coloring matter in the form of hematite; these 

 constitute this clastic rock, which is not much, if any, metamorphosed beyond 

 compact consolidation. 



Two sections. 



Age. . Upper Keewatin(?) N. H. w. 



No. 505. GRAYWACKE. 



Two miles north of Carlton, on the railroad grade, at a long rock cut. 

 Ref. Annual Report, x, pages 17, 19, 29. 



Meg. Hard, gritty graywacke. 



Mic. Angular, frequent grains of quartz, fel<Lyar of several kinds, and a few 

 of jaspilyte, are embraced in the usual more or less clouded matrix, which consists 

 of chlorite, calcite and fine quartz and feldspar debris. 



One section. 







Age, Keewatin(?) N. H. w. 



