US THE GEOLOGY OP MINNESOTA. 



[Diabase. Aporhyolyte. Quartz. 



No. T)4. DIABASE. 



East Duluth. From a dike three and one-half feet wide, associated with others, cutting No. 53 in a direc- 

 tion N. 50 E., forty rods east of No. 53B. 

 Ref. Annual Report, ix, page 19. 



Mey. A black, fine-grained diabase. 



Mic. Lath-shaped feldspars occur imbedded in augite, alteration products of 

 the same, and black opaque material, much of which is ntnytiefite. 

 One very poor section. 



Aye. Probably Manitou. IT. s. G. 



No. fio. APORHYOLYTE. 



East Duluth. In the bite of a little bay, continuing half a mile, by the coast, becoming broken and 

 slightly amygdaloidal. It is reddish, angularly and linely jointed, sometimes a jaspery-looking rock; overlies 

 No. 54; sometimes dips at 60 N. E. 



Ref. Annual Report, ix, pages 19, 20; Bulletin ii, page 118. 



Mic. This rock is like the red elements in No. 53B, but is finer grained. This 

 remark applies to the gray, or slightly reddish-gray, portions, of which one section is 

 examined. 



Another section, numbered 55, and evidently from that part of No. 55 which in 

 the field description was considered jaspery, is almost wholly red, but had originally 

 amygdaloidal spots which are now filled with qnartz having various orientation. 



Quartz is also otherwise widely disseminated. This is a finer-grained rock than 

 the last, but evidently a portion of the same mass more altered. 



Two sections. 



Age. Cabotian. N. H. w. 



No. 55A. QUARTZ (from X. ~>~> in concretions.} 



Duluth. Same locality as No. 55. 

 Ref. Annual Report, ix, page 19. 



Meg. A red-brown, very fine-grained, earthy rock, irregularly blotched with 

 darker areas. Scattered through the rock are areas of quartz mixed with and sur- 

 rounded by brick red material, which is a little redder in color than the main mass 

 of the rock. A few small porphyritic red feldspars are also seen. 



Mic. The section is very thick, but seems to show a rock essentially like No. 

 50. The section shows one area of coarsely crystalline quartz into which extend 

 small prisms of a brown to black opaque substance, which in reflected light is red like 

 the mass of the rock. These prisms in outline and general relation to the rock and 

 to the quartz remind one of the epidote crystals which are so common in such situa- 

 tions, and it is not impossible that they are altered epidotes. There is, however, no 

 trace of the original epidote substance in any of the prisms. 



One section. 



Age. Cabotian. u. s. G. 



