THE GEOLOGY OF MINNESOTA. 



[Quartzy te. Taconyte. Greenstone schist . 



NO. 2140. QUARTZYTE. 



Mountain Iron mine, Mesabi Iron range. Same place as No. 2139. 



Ref. Annual Report, xxi, page 160, rock d ; Annual Report, xxiv, page 48. 



Meg. Coarser than No. 2139. 



Mic. The boundaries of the original clastic grains are marked off from the 

 secondary additions by the usual line of colored impurities. The original grains vary 

 considerably in size and are accompanied, as in No. 2139, by a fewtriclinic feldspars. 

 Between the quartzes, and sometimes staining them within, is a gray-greenish sub- 

 stance which appears to be chlofitized hornblende. This substance, under favorable 

 conditions, has a slight polychroism. This hornblendo-chloritic greenish substance 

 sometimes takes the form of a spongy, gray mass in which lie many angular grains 

 of quartz, and sometimes it forms small spaces without containing quartzes. It 

 then suggests the possibility of its being of the nature of devitritied volcanic ash. 

 One section. 



Aye. Animikie (Pokegama). N. H. w. 



No. 2141. TACONYTE. 



Mountain Iron mine, Mesabi Iron range. 



Ref. Annual Report, xxi, page 160, rock e ; Annual Report, xxiv, page 48. 



Meg. Quartzyte, with large per cent of iron ore. 



Mic. This rock is wholly of secondary origin in its present condition, the quartz 

 forming about one-half, and interlocking in the characteristic mosaic manner of 

 taconyte. Some of the taconitic globules are nearly wholly opaque with iron, and 

 some are composed of an exceedingly fine mosaic of quartz undistinguishable from 

 the flint or devitrified silicified glass of Gunflint lake, and the same as seen in No. 

 2138. One section. 



Age. Animikie (iron-bearing member). N. H. w. 



No. 2145. GREENSTONE SCHIST. (Pebbly. ) 



S. W. % N. E. % sec. 36, T. 64-11, Saturday lake, south from the east end of the portage from Pall lake; 

 a low bluff. 



Ref. Annual Report, xxiv, page 49. Compare rock No. 175W. 



Meg. Appearing greenish, pebbly and occasionally sericitic. Pebbles mostly 

 less than three inches in diameter, but reaching eight to ten inches. 



Mic. Abundant fine grains of epidotc lie in a chloritic, hornblendic and calca- 

 reous matrix, associated with some cubes of pyrite. The structure is decidedly 

 schistose. The small glassy feldspars are of secondary generation, but the larger 

 feldspars, plainly clastic in origin, are dim and decayed. One section. 



Age. Archean (Keewatin). N. H. w. 



