PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 267 



Aporhyolyte. Gabbro.] 



quartz. No olivine is visible. The augite but rarely shows any tendency to become 

 diallagic. The following extinctions were measured on the feldspar, indicating a 

 labradorite: Extinction on n f , 56; extinction on n v , 55; angle on n p , between the 

 pericline and albite bands, 81 (Fouque, Bulletin de la Societe de Mineralogie de 

 France, vol. xvii, page 428). 



Two sections. 



Age. Cabotian; Beaver Bay diabase (?). It is at present impossible to affirm 

 either the Cabotian or the Manitou age of this rock. For the sake of consistence, 

 with what precedes, this is classed Cabotian; but it may be later than the basal con- 

 glomerate of the Potsdam. More field work is needed to determine this point. 



N. H. w. 

 No. 224. APORHYOLYTE (?) 



From the rocky point which divides Double bay into two parts; N. E. % S. E. J sec. 10, T. 62-4 E. This 

 rock is somewhat basaltic like trap, and also rudely bedded. 

 Ref. Annual Report, ix, page 57. 



M.ey. A fine-grained, brown rock, very indistinctly mottled with a darker color. 

 Under the lens the rock appears granular, but the only mineral distinguishable is 

 feldspar. 



Mic. The section, which is quite fine grained, is made up of feldspar, quartz, 

 green hornblende, hematite, magnetite, chlorite and augite( ?). The feldspars are more 

 or less cloudy, are mostly untwinned, and are frequently in short, stout crystals, 

 although many of the grains are allotriomorphic. The quartz is in small grains and 

 sometimes in small poikilitic areas. The hornblende is in small plates, and is evi- 

 dently secondary. The grains, which are perhaps augite, are minute, greenish to 

 colorless, and polarize brightly. In a few places there is a little greenish to brown- 

 ish interstitial matter which, under crossed nicols, is dark, except for a few light 

 points. It probably represents glass. Other areas, which appear similar to this inter- 

 stitial material in ordinary light, under polarized light are seen to be largely feld- 

 spathic. The rock as a whole is considerably altered. 



One section. 



Age. Cabotian. 



Remarks. See under No. 226. u. s. G. 



No. 225. GABBRO (with orthoclase). 



From the most easterly point of Double bay. (See Nos. 5, 263.) 

 Ref. Annual Report, ix, page 57; Bulletin ii, page 81. 



Mey. A coarsely crystalline "orthoclase gabbro" (apparently), as defined by 

 Irving, comparable to that form of the gabbro at Duluth, which is represented by 

 No. 5 of this series. 



