818 THE JOURNAL OF GEOLOGY. 



green enstatite, olivine and magnetite. " Even in the same hand 

 specimen it passes from a fine schistose condition into a coarse 

 crystalline one, while in some of its modifications it assumes the 

 character of a regular quartzite." The schistose portion " shows 

 an admixture of well-defined tabular plates of yellowish-green 

 enstatite, and granular or 'fractured' olivine of a paler shade. 

 The enstatite exhibits an exceedingly fine striation, and it con- 

 tains no enclosures, except a few grains of magnetite. It 

 polarizes brilliantly, but shows no pleochroism. The olivine 

 is more abundant than the pyroxene. It is present in the form 

 of angular masses and grains, which have a fragmental appear- 

 ance as if crushed by mechanical pressure or in consequence of a 

 sudden thermal disturbance. The magnetite occurs in rounded 

 grains and crystals, varying from dust-like minuteness to aggre- 

 gates equaling in size the largest of the enstatite tablets." 



Titaniferous Magnetites. — The specimens in the possession of 

 the United States Geological Survey all contain a large proportion 

 of magnetite, which in some cases runs so high as to constitute 90 

 per cent, of the entire rock. These latter rocks have the bright 

 metallic lustre of magnetite and usually a finely granular texture. 

 The lustre frequently becomes very brilliant and the specimen 

 takes on the peculiar pinkish tinge of ilmenite. A careful inspec- 

 tion of such specimens as seem to be pure ore, reveals the pres- 

 ence in them of tiny yellowish green grains of olivine, but these 

 are so rare that they produce but little impression on the general 

 aspect of the rock. When the magnetite makes up practically 

 its entire body, the rock is much jointed, and, consequently, 

 it easily breaks into small irregular or cuboidal fragments, as 

 Winchell has already noted, and these are not unfrequently nat- 

 ural magnets. Tests of magnetites of this kind from the shores 

 of Little Sasaganaga Lake, N. W. % Sec. 7, T. 64 N., R. 5 W., prove 

 them to be very rich in titanium, as was surmised from their 

 pinkish tinge. 



Professor Winchell 1 cites several analyses of titaniferous mag- 

 netites from the north edge of the gabbro area, that show from 2.23 



'Bull. No. 6, Minn. Geol. Survey, p. 141. 



