548 THE GEOLOGY OF MINNESOTA. 



[Diabase. 



Meg. A very fine-drained, very dark, greenish-gray rock, compact and resembling 

 a fine-grained diabase. 



Mic. The section is composed of small, much kaolinized plagioclase laths, 

 arranged by flowage, augite and much niiif/i/d/te. The augite is thickly set with 

 minute grains of magnetite and has altered in places to a confused mass, rich in 

 magnetite. It is possible that some of these apparent altered augite areas represent 

 an original unindividualized base. 



One section examined. 



Age. Cabotian. u. s. G. 



No. 792. DIABASE. 



Poplar river; N. E. % sec. 20, T. 60-3 W. From the foot of a precipitous hill facing north; part of the 

 Sawteeth mountains. This sample is probably from the place known locally as "the rock pile." Compare 

 No. 455E. 



Ref. Annual Report, x, page 105. 



Meg. A medium-grained, dark, yellowish-gray diabase. 



Mic. The section shows chiefly plagioclase laths and augite, the latter later 

 than the former and commonly in ophitic plates of considerable size. There is much 

 secondary, green, chloritic material, also some Magnetite. A few yellowish-brown 

 areas (bowlingite?,) are present; these are probably the results of alteration of olivine 

 or original augite. 



One section. 



Age. Cabotian. u. s. G. 



No. 793. DIABASE. 



From the foot of the last hill (nearest lake Superior) on the west side of Poplar river; 600 feet above the 

 lake. Probably in N. E. % sec. 29, T. 60-3 W. 

 Ref. Annual Report, x, pages 105, 106. 



Meg. A rather fine-grained, yellowish-brown diabase. 



Mic. The section is considerably altered and has much yellowish and greenish 

 alteration material, also, some secondary quartz. There ai-e small laths of p/agiorfaxe 

 and augite, the latter not in ophitic grains, but, in part at least, later than the feld- 

 spar. Some olivine, or the alteration product of olivine, is present; also mayitr/ife 

 and hematite. One section. 



Age. Cabotian. u. s. G. 



No. 794. DIABASE. 



"From the same hill [as No. 793], one-fourth way uj>." 

 Ref. Annual Report, x, page 1C6. 



Meg. Similar to No. 793. 



Mic. Similar to No. 793, but not quite so much altered. One section. 



Age. Cabobian. u. s. G. 



