830 THE GEOLOGY OF MINNESOTA. 



[Quartz. Granite. Diabase. 



M >. The quartz grains are very tine, but they have a structure of elongation, so 

 that the mass has a roughly fibrous aspect. Within the quartzyte mass, however, 

 are a few feldspathic grains, one being distinctly of microcline, while other grains are 

 of calcite. The appearance of elongation is due not so much to the elongation of the 

 individual quartz grains as to their rather uniform orientation in belts that run 

 roughly parallel, causing light and dark to alternate in belts on rotation. One 

 section. 



Age. Inclusion in the Archean granite of Saganaga lake. N. H. w. 



No. 2049. QUARTZ. ( Vein.) 



Within a few feet of No. 2048, in the Saganaga granite. 

 Ref. Annual Report, xxiv, page 23. 



Meg. Vitreous quartz from a vein. 



Mic. This has a remarkable contrast with No. 2048, being in large plates that 

 have the characteristic uniform polarization and extinction. One section. 



Age. Vein in Saganaga granite. 



Jiennirk. The differences which these quartzes present indicate different 

 origins or different histories, and perhaps both. No. 2049 is plainly from an ordinary 

 vein of quartz, and so it appeai-s in the rock in place. No. 2048 has not the form 

 nor manner of a quartz vein in the rock, but rather of an irregular patch, and under 

 the microscope it has none of the characters of vein quartz. N. H. w. 



No. 2050. GRANITE. 



Same place as Nos. 2048 and 2049. 

 Ref. Annual Report, xxiv, page 23. 



Meg. Granite in which occur the foregoing quartzes. 



Mic. This is an ordinary, but considerably altered, granite, containing epidote 

 (included occasionally within the feldspars), hornblende, xjdiene, with the usual feld- 

 spars and quartz. One section. 



Age. Archean (granite). N. H. w. 



No. 2051. DIABASE, (roi-^lujritic.) 



S. E. Yi sec. 24, T. 65-4 W., west from Gunflint lake. From the high, isolated hill north of the railroad : 

 forms a sill. 



Ref. Annual Report, xxiv, page 26. (Compare Part I, page 66.) 



Meg. Diabase with coarse, sporadic feldspar crystals and with larger groups of 

 Hner crystals which form feldspar rock or anorthosyte. 



Mic. The pyroxene is converted mostly, but not wholly, to hornblende, which 

 shows still the ophitic relation to the smaller feldspars. The large feldspars are 

 considerably affected by the development of mica. The specimen collected is illus- 

 trated by plate IV, figure 2. One section. 



Age. Cabotian. N> Hi Wj 



