814 THE GEOLOGY OP MINNESOTA. 



[Green wacke. Aporhyolyte. Pebbles. Granite. 



No. 1967. GREENWACKE. (Tuff?) 



Same place as No. 1966. 



Kef. Annual Report, xxii, page 17. 



Mey. Sample of the roughly conglomerate-appearing portion of the same rock 

 mass as No. 1966. 



Mic. There are certain spots in which the green amphibole prevails over all 

 the other minerals, even to their entire exclusion, and others in which magnetite 

 plays the same role. The former are sometimes irregularly angular, and bordered 

 by a band of greater abundance of granular magnetite; in other places the magnetite 

 simply fades out and leaves a somewhat roundish area in which none is found. On 

 the other hand magnetite sometimes suddenly increases in innumerable fine grains, 

 forming a tache something like lapillitic magnetited fragments seen in old volcanic 

 ash. One section. 



Aye. Animikie(?) N. n. w. 



No. 1968. APORHYOLYTE. 



Same place as the last but a short distance further west, near the creek crossed by Piedmont avenue, 

 Duluth. 



Ref. Annual Report, xxii, page 17. 



Meg. Red rock, associated with the foregoing black rock. 



Mic. Poikilitic quartz spreads irregularly throughout the fine mass, embracing 

 the red (feldspathic?) material. It consists of numerous crystal orientations. 

 Magnetite, hornblende and epidote are likewise more or less abundant, the hornblende 

 being quite scant. One section. 



Age. Cabotian. N. H. w. 



No. 1976. PEBBLES. 



Pebbles from the crumbling red conglomerate which overlies the green shale (No. 1974) and the quartzose 

 conglomerate, at the mouth of the creek entering th<* St. Louis river on S. W. % sec. 1, T. 48-1G W. 

 Ref. Annual Report, xxiii, pages 239, 240. 



Meg. The pebbles are not usually more than an inch in diameter. They are of 

 various kinds of rocks, among which are: greenish-gray shale; gray, flinty rock; 

 reddish, banded, flinty rock; pyrite; vein quartz; fine-grained, red granite; red 

 quartzyte; fine-grained, decayed, reddish, igneous rocks. 



Age. Potsdam conglomerate. u. s. o. 



No. 1980. GRANITE. 



Ortonville, near Big Stone lake. Much used for construction. 

 Ref. Annual Report, xxiv, page 1. 



Meg. Rather coarse, reddish, sometimes porphyritic. 



Mic. Microdine and orthodase form large crystals. Quartz is abundant; biotite 

 is rather sparse but preceded both feldspars. The orthoclase sometimes enters the 



