PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 885 



Chlorite. Copper . ] 



6. The finer the grains the more they were decayed, and the less evident they 

 have become after the regeneration. 



7. They are both orthoclastic and plagioclastic, a fact which can be explained 

 by reference to an original clastic accumulation, but hardly by simultaneous crys- 

 tallization from a homogeneous molten magma. One section. 



Age. Lower Keewatin(?) 



Remark. It should not escape notice that this rock, here supposed to belong in 

 the Lower Keewatin and to have contributed to the formation of the Stuntz 

 conglomerate of the Upper Keewatin, is petrographically identical with much 

 of the quartz-porphyry and granitic intrusive rocks, already described, occurring 

 between Moose and Flask lakes, supposed to be intrusive in the Upper Keewatin, viz.: 

 Nos. 2263, 2264, 2265, 2266, and is also structurally and genetically the same appar- 

 ently as the quartz-porphyi'y of Kekequabic lake, which is also supposed to be intru- 

 sive in the Upper Keewatin. Therefore, the assignment of this to the Lower Keewatin 

 must be with some uncertainty. N. H. w. 



No. 2277. CHLORITE. (Massive, ripidolitc. ) 



In vug-like angular spaces of No. 2276, as exposed on the weathered surface. 

 Ref. Annual Report, xxiv, page 84. 



Meg. Very fine grained, green; hardness about that of chlorite; massive. 



Mic. The mass of this substance, when viewed with high power objective, is 

 resolved into little groups of very low doubly refracting scales or fibres, which are 

 placed divergently and irregularly together. They extinguish parallel and have a 

 negative elongation. Their effect is to make the field of the microscope rather dark. 



A micro-chemical preparation with hydro-fluosilicic acid affords numerous 

 microscopic rhombohedrons of more or less irregular development, but with perfect 

 edges and faces. These may be, and probably are, silicic fluorides of magnesium 

 and of iron.* The species is probably ripithlite, owing to the position of the 

 axis ( g ) with relation to the lamellae, and the tendency of the clusters to assume 

 vermicular forms. One section. 



Age. In vugs in No. 2276. 



Remark. In this chloritic mass are a very few Muscovite scales, which are as 

 fine as those of the ripidolite, and are arranged parallel with them. N. H. w. 



No. 2278. COPPER. (Metallir. ) 



Montana shaft of the Minnesota Iron company, Soudan. 



Ref. Annual Report, xxiv, page 84 : Proceedings of the Lake Superior Mining Institute, iv, 70, 1896. 

 Compare No. 2272. 



Mey. Occurs in a vein-like sheet, which crosses the ore deposit diagonally, and 

 dips eleven or twelve degrees toward the south, encountered in mining iron at the 



* The elements of a new method of chemico-microseopic analysis of rocks and minerals. EMANUKL BORICKY. Translated 

 in \iiu'l<cnti( Minnrxotit llcjiort (for 1890). 



