802 THE GEOLOGY OP MINNESOTA. 



[Gabtoro. Keratophyre. 



and the characters of the hornblendes, as well as the confused aspect of all the 

 minerals interstitial between the large phenocrysts, carries the impression that this 

 rock at first was largely composed of zirkelyte. There is no evidence of orthoclase 

 in the rock, but the old feldspars are wholly triolinic and quite likely of labradorite. 

 They enclose considerable epidote. One section. 



Age. Cabotian. . N. H. w. 



No. 1867. GABBRO (with orthoclase). 



S. E. HS-W.% sec. 24, T. 63-3 W.; south of Brute lake. 

 Ref. Annual Report, xxii, page 10. 



Meg. A medium-grained, gray, granitic rock, composed of whitish to reddish 

 feldspar, augite, hornblende and magnetite. No section. 



Age. Cabotian. u. s. G. 



No. 1869. GABBRO (ivith ortlwclase). 



South side of the island in N. E. % S. W. % sec. 24, T. &3-3 W.; Brute lake. 

 Ref. Annual Report, xxii, page 11. 



Meg. A rock similar to No. 1867, but considerably finer grained. 

 Age. Cabotian. u. s. G. 



No. 1870. GABBRO. 



East end of the island, S. W. ^ N. E. J^ N. E. M sec. 13, T. G3-3 W.; Brute lake. 

 Ref. Annual Report, xxii, page 11. 



Meg. Medium-grained rock, rich in feldspar. 



Mic. The augite preceded or was cotemporary with the feldspars. Olivine is 

 nearly lost in a serpentinous decay, and the feldspars, which are coarse and compose 

 the most of the rock, are. also much altered. One section. 



Age. Cabotian. N. H. w. 



No. 1874. GABBRO. 



South side of a small lake, N. E. % N. E. % sec. 17, T. 63-2 W., near Brute lake/ 

 Ref. Annual Report, xxii, page 11. 



Meg. Dark porphyry. 



Mic. The large feldspars, by their extinctions, seem to approach andesine, but 

 the rock is not noticeably different from No. 1870. One section. 



Age. Cabotian. N. H. w. 



No. 1876. KERATOPHYRE (?) 



N. E. J N. E. % sec. 20, T. 63-3 W., Brute lake. 

 Ref. Annual Report, xxii, page 11. 



Meg. Dark, compact, fine grained, with a tendency to reddish color. Small 

 dark areas of crystalline material, surrounded by a vein of i-ed which grades into the 

 rest of the rock, are common. 



