474 THE GEOLOGY OP MINNESOTA. 



[Diabase. Granite. Apotrachyte. 



No. 654. DIABASE. (Fine grained. ) 



"This sample is from a ridge rising about one hundred and seventy-live feet, crossed by the section line 

 running east, S. E. 1^ sec. 18, T. 63-2 E." 

 Ref. Annual Report, x, page 69. 



Meg. A very fine-grained, dark, greenish-gray rock of uniform composition, 

 except for a very few areas of sub-porphyritic feldspar. 



Mic.' The section is composed essentially of feldspar andatigite. The former is 

 in small lath-shaped individuals which are polysynthetically twinned; equal extinc- 

 tion angles in sections normal to 010 are as high as 33, indicating labradorite. The 

 augite is in small grains between and within the feldspar laths, and only rarely do 

 larger grains, showing a tendency to the ophitic texture, appear. The slide also 

 shows magnetite and a green alteration product which, perhaps in part, represents 

 original olivine. 



One section examined. 



Age. Cabotian. 



Remark. This rock, quite probably, is a dike rock cutting the earlier gabbro 

 and red rock, but whether it is of Cabotian or Manitou age is uncertain. It resembles 

 so.me of the Keweenawan dike rocks found on the lake Superior shore. u. s. o. 



No. 655. GRANITE. (Red, fine grained.) 



N. E. J4 sec. 20, T. 63-2 E. Appears in a low ridge: 

 Ref. Annual Report, x, page 69. 



Meg. A fine-grained reddish rock, somewhat mottled and of a porous texture. 

 The cavities, which are irregular in outline, are more or less filled with quartz and a 

 dull green earthy mineral (perhaps chlorite). 



Mic. The section shows one of the usual fine-grained "red rocks" composed of 

 quartz, reddened feldspar, magnetite, hematite and yellowish alteration products. 

 Micropegmatyte is common. 



One section examined. 



Age. Cabotian. u. s. G.. 



No. 656. APOTRACHYTE. 



A short distance east of No. 655. 

 Ref. Annual Report, x, page 69. 



Meg. A fine-grained reddish rock of porous texture. Many small light-gray 

 porphyritic feldspars are present. Macroscopically this rock is quite similar to No. 

 655, but lacks the quartz. 



Mic. A few small, much altered, porphyritic feldspars are seen in a fine-grained 

 groundmass composed of a confused aggregate of quartz, reddened feldspar, magnetite 

 and hematite. In the section there are a number of sharply outlined cavities. 



One section examined. 



Age. Cabotian. u. Sg G 



