15S THE GEOLOGY OP MINNESOTA. 



[Amygdaloid. Dialtasr. Sandstone. 



No. 70. AMYGDALOID. (,SV7/<y//vw. ; 



Near Lester river, on the west side, forming a prominent point or break in the coast line; overlies No. 69. 

 Ref. Annual Report, ix, page 22. 



Mr//. Apparently a fragments! rock, containing rounded pebbles (?) of quartz 

 with a dark, fine-grained matrix, in which is disseminated much pyrite in the form of 

 cubes, as well as some calcite. 



Mic. The matrix proves to be trachytic with feldspars, which have independent 

 tabular forms in the midst of the other minerals. The pyroxenic element, which was 

 probably augite, is changed to secondary products, which are dark, in general, with 

 imit/Hi-flfi'. There are other areas which now give a blue tint between the crossed 

 nicols t jii'in/iiH' ), which seem to have consisted of oliriiir. The rounded quartz areas 

 are probably fillings of vesicular cavities in the original rock. They consist of 

 numerous interlocking grains of different orientation and sometimes are very finely 

 granular. Other cavities are filled with m/rifr. 



Two sections. 



Aye. Cabotian. N. H. w. 



No. 71. DIABASE. (Finegrained.) 



Near Duluth.- Just west of the mouth of Lester river. Overlies No. 70. Continues but six or eight rods 

 and disappears under the beach, and nothing appears again till at Lester river. 

 Ref. Annual Report, ix, page 22. 



Mc<j. A fine-grained dark brownish rock, composed of small feldspars and a 

 darker material. Many of the feldspars appear pinkish. A very few small porphy- 

 ritic plagioclases are present. 



Mir. Small lath-shaped /A////V^7ff.sr.s and an abundance of amjifc and nini/nrfitf. 

 The augite is largely still quite fresh. A hematite stain has penetrated the rock and 

 is more abundant in the vicinity of the magnetite grains. 



One section. 



Aye. Cabotian. u. s. G. 



No. 72. SANDSTONE. (Fiji-<><-/tit<ti<- ;/rit.) 



Mouth of Lester river, east of Duluth. This river was called Passabika by Dr. Owen. 

 Ref. Annual Report, ix, page 22. 



Mi'//. Apparently a granular clastic fine-grained rock, of a brown or reddish 

 color, homogeneous and thinly bedded. The amygdaloidal structure does not pervade 

 the sandrock, but it pervades the cement or rock which fills the angular openings 

 between the pieces of the breccia. 



Mir. The section made from the clastic rock shows a fine grain, the individual 

 grains being both rounded and angular, and of different sorts. The most evident 

 and conspicuous are angular limpid fragments of quartz. These are covered with 

 a coating which is now stained as by hematite. Other grains which now consist 



