PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 197 



Gabbro. Stilbite and calcite.] 



ures were generated in a magma before complete cooling, or as a consequence of 

 original rapid cooling, in which case the German nomenclature would impose on this 

 rock the name granophyre, the French equivalent being micropegmatoid. It is 

 probable that by Irving it would have been placed with the felsytes. N. H. w. 



No. 131. GABBRO. ((irminiUic,.) 



Beaver Bay. From a point six rods northeast of No. 130. 

 Ref. Annual Report, ix, page 33. 



Meg. A dark fine-grained rock similar to No. 122. 



J//V. The section is composed of plagioclase, pyroxene, magnetite, biotite, 

 apatite and green alteration products. The plagioclase is in part idiomorphic and 

 partly allotriomorphic, the structure of the rock being granular. Some of the plagio- 

 clase is clear, shows no twinning and no cleavage and might be mistaken for quartz. 

 A number of such grains were examined, but no quartz was found. The pyroxene 

 (probably diallage) is in minute rounded grains. Some of the smaller grains may 

 possibly be olivine, but this point cannot be determined definitely because of the 

 small size of the grains and the thickness of the section. The rock, as a whole, is 

 similar to No. 122, but that rock has more of the idiomorphic plaigoclases than the 

 one here considered. 



One section. 



Age. Cabotian. 



Remarks. Consult Part III for a statement of the structural relations of the 

 various rocks occurring in the vicinity of Beaver bay. u. s. G. 



No. 131A. STILBITE AND CALCITE. 



Incrustations on openings in No. 131. Beaver bay. 

 Ref. Annual Report, ix, page 33. 



The incrustation consists of two minerals interlayered with one another. 

 One is white, and consists of calcite. The other is brownish red and has a radiated 

 crystallization, becoming tabular. The two minerals are also intermixed irregularly. 

 In powder the wedge-shaped cleavage pieces of the red mineral extinguish nearly or 

 quite parallel with their principal elongation. Good cleavage pieces, however, have 

 this extinction at 5 to 7, and they also show the emergence of an optic normal in 

 convergent light. The optic plane is therefore parallel to the easy cleavage. These 

 characters sufficiently indicate stilbite. Still, a test was made for gelatinous silica in 

 hydrochloric acid, without result, and another, by the Boricky method, with hydro- 

 fluosilicic acid, which gave numerous crystallitbs of fluosilicates of lime in a great 

 variety of forms. 



One section; two preparations. 



Age. Vein in Cabotian anorthosyte. N. H. w. 



