PETROGBAPHIC GEOLOGY AND DESCRIPTIONS. 303 



Gabbro. Qnartzyte.] 



Mic. The section shows a granular rock composed mostly of quartz and reddened 

 feldspar. The other minerals present are biotite, chlorite, epidote, calcite, pyrite, mag- 

 netite&nd hematite. Quartz is in grains and also in pegmatitic intergrowths with the 

 feldspars, especially around the peripheries of crystals of the latter mineral. 



Chemical analysis. The following analysis was made by professors J. A. Dodge and C. F. Sidener: 



SiO 2 01.09 



AljO 3 15.34 



Fe 2 O 3 5.74 



FeO 3.69 



CaO 3.10 



MgO 1.33 



Na 2 O 3.41 



K 2 O 3.65 



H 2 O - - 1.80 



Total 99.15 



The analysis shows a lower percentage of silica than would be inferred from the 

 large amount of quartz in the sections. In chemical composition this rock is more 

 basic than the granular red rock described by Bayley from this locality,* and probably 

 this hand sample would belong with the rock intermediate between the granular red 

 rock and the gabbro. A considerable part of the lime shown in the analysis can be 

 accounted for by the presence of calcite, and with this in mind it seems probable 

 that the feldspar is largely anorthoclase, the feldspar common to the granular red rock. 



Age. Cabotian. u. s. G. 



No. 293. GABBRO (with olivine). 



From the north side of Pigeon point a mile and a half east of the mouth of Pigeon river. This rock forms 

 the coast line, which rises sometimes fifty feet above the lake, nearly all the way from the extremity of the point 

 and is doubtless in continuation from No. 291 and from No. 287. 



Ref. Annual Report, ix, pages 50, 70. 



Mic. The thin section made from this rock presents a fresher appearance than 

 those from No. 291, and contains much fresh olivine, a little biotite and chlorite with 

 characteristic aureoles. The auaite is more frequently ophitic than in No. 291, 

 indeed it is generally ophitic, and at this point therefore this rock hardly deserves 

 the name gabbro. 



Two sections. 



Age. Cabotian. N. H. w. 



No. 294. GABBRO (with olivine). 



From the hills next north of the glacier plain on the Grand Portage trail, probably S. E. % sec. 30, T. 

 64-6 E., near the point where the Arrow River trail crosses them. This rock is identical with rock No. 293. 

 Kef. Annual Report, ix, pages 72, 73. 



No. 295. QUARTZYTE. 



Near upper end of the Grand portage; probably in N. E. } sec - 29, T. 64-5 E. 



Ref. Annual Report, ix, page 73. (See, also, rock No. 772 [W.] from this same locality.) Annual 

 Report, xvi., page 291; Final Report, iv, page 510. 



* U. S. Geol. Survey, Bulletin cix. 



