164 THE GEOLOGY OP MINNESOTA. 



[Diabase. Amygdaloid . 



A i/i'. Cabotiau. 



IiriiKirk. This rock undergoes variations between the lake shore and the old 

 French River mining location, becoming amygdaloidal, and also in other places 

 finer grained, even aphanitic, as if it had been glassy. Of two sections made from 

 the rock at the old mine, on the veinings of which prehnite forms coatings, one is 

 permeated with jtrc/nt/fe, as well as having small vesicles that are completely filled 

 with the same mineral. N. H. w. 



No. 82. DIABASE (with oliriiif). 



French river, one half mile from the lake. An amygdaloidal portion of No. 81. 

 Ref. Annual Report, ix, page 23. 



Mcy. A dark brownish rock of very fine grain. Contains amygdules of laumo- 

 tite, prehnite and a dark mineral (chlorite). The rock also has small indistinct 

 black areas, which are probably largely of chlorite. 



Mir. The section is almost exactly the same as the first section described under 

 No. 81, and so needs no further descriptions. The feldspars are perhaps a little 

 larger than in No. 81. 

 One section. 



Age. Cabotian. u. s. o. 



No. 83. DIABASE. (Altcml. ) 



French river. 



Ref. Annual Report, ix, page 24. 



Meg. There are two hand specimens. One is a dark purplish rock, similar to 

 Nos. 81 and 82. It contains amygdules, veins and geodic cavities of prehnite. The 

 other hand sample is part of a geodic cavity filled with coarsely crystallized laumon- 

 tite and some prehnite. Part of the rock surmounting the geode is present; this is 

 similar to the other sample, but is redder and decayed. 



Mic. The section shows a rock which was undoubtedly originally very similar 

 to Nos. 81 and 82, but is now highly altered. The outlines of the small lath-shaped 

 J'c/i/sjun-N are sharply preserved, but the whole rock, except the areas of iron ore and 

 some opaque substances, has been replaced by jirr/nufc. From the hand sample, 

 which is apparently quite fresh, one would not suspect that so profound a change 

 had been wrought in the rock. 



Two sections. 



Aije. Cabotian. r. s. G. 



No. 84. AMYGDALOID. 



A mile and a half up French river. Allied to the series of traps and amygdaloids already described at 

 this place. 



lief. Annual Report, ix, page 24. 



No section. 



Age. Cabotian. N. H. w. 



