482 THE GEOLOGY OF MINNESOTA. 



[Diabase. Granite. Galibro. 



NIC. The section shows small lath-shaped feldspars and large ophitic auyites, 

 also magnetite and the usual alteration products. Some of the altered areas may 

 quite probably represent original olivines. The section resembles that of No. 665. 



One section examined. 



Age. Cabotiau. u. s. G. 



No. 670. DIABASE. (Coarse*) 



"From one-fourth mile south of lake Abita, in the large hill over which the trail passes." N. E. ^ N. E. 

 % sec. 28, T. 63-1 W. 



Ref. Annual Report, x, page 74; Bulletin ii, pages 76, 95. 



Meg. M. E. Wadsworth's description of this rock is as follows:* "It is a rusty 

 brown coarsely crystalline rock, discolored by surface weathering. Composed mac- 

 roscopically, chiefly of brownish ferruginous stained feldspars and dark silicates 

 traversed by hexagonal apatite needles. " 



Mic. " The section is composed of feldspar (plagioclase chiefly) pyroxene, 

 secondary hornblende, and magnetite. Much limonite occurs, lining the fissures and 

 staining the feldspars. The pyroxene is brownish and has the characteristic fractures 

 and general characters of augite, but in portions of its mass the structure of ilialhigc 

 is clearly to be observed, as a secondary structure arising through the alteration of 

 the augite. " 



One poor section examined. 



Age. Cabotian. u. s. G. 



No. 671. GRANITE (with augite). 



From the hill near the south shore of lake Abita; S. E. % S. E. ^ sec. 21, T. 63-1 W. Not certainly in 

 place. 



Ref. Annual Report, x, page 74. 



Meg. A reddish-gray rock of rather fine granitoid texture. The minerals are 

 quartz, feldspar and a black mineral (augite). 



Mic. One of the characteristic red rocks, but having some augite still remaining. 

 This section is similar in general character to No. 668. 



One section examined. 



Age. Cabotian. u. s. G. 



No. 672. GABBRO (with hornblende). 



From the same locality as No. 671, but near the top of the hill. 

 Ref. Annual Report, x, page 74; Bulletin ii, page 78. 



Meg. A coarse-grained gray rock, granitoid in texture and composed of flesh- 

 colored and gray feldspar, magnetite and a black substance (mostly augite). 



Mic. M. E. Wadsworth's description of this rock is as follows :f "The section 

 is composed of partially altered plagioclase, augite partially changed to diallage, 



*Sulletin ii, p. 76. 

 ^Bulletin ii, p. 78. 



