PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 808 



Basalt. Diabase.] 



Mic. Fine, angular quartz grains, sometimes interlocking, and occasionally 

 rising to larger size, representing bipyramidal crystals, lie in a finer matrix of about 

 the same materials. There are roundish spots of larger size, with iron-stained periph- 

 eries, now occupied with pennine which may have the nature of amygdaloidal cavities. 

 A few small crystals and parts of crystals of a triclinic feldspar are disseminated 

 through the fine matrix. There are visible in the slide a few small grains of sphene, 

 also others of ilmenite, partly altered to leucoxene, and of epidote and apatite. One 

 section. 



Age. Cabotian(?) 



Remark. The nature and origin of this rock it is difficult to establish by the 

 microscope alone. It may be, however, composed of a mingling of the basic and 

 acid elements. N. H. w. 



No. 1879. BASALT. 



On a small island in N. W. M S. E. % sec. 18, T. 63-3 W., Brute lake. 

 Ref. Annual Report, xxii, page 11. 



Meg. Black rock, so-called. 



Mic. The structure of this rock is very dense and indistinct, and is further 

 obscured by alteration, while considerable magnetite is a cause of its dark color. It 

 seems to have been to some extent a basic glass. With the exception of some traces 

 of the early feldspars, nothing of its original composition remains, but hornblende, 

 epidote, sericite, chlorite, have taken its place. One section. 



Age. Cabotian. N. H. w. 



No. 1880. BASALT. 



Western outlet of Brute lake, N. E. M S. W. % sec. 18, T. G3-3 W. 

 Ref. Annual Report, xxii, page 11. 



Meg. Spotted phase of the rock No. 1879. 



Mic. This rock is more altered to epidote, which appears in the areas formerly 

 occupied by the supposed basaltic glass, and hornblende is almost wanting. One 

 section. 



Age. Cabotian. N. H. w. 



No. 1881. DIABASE. (Coarse.) 



In a low ridge crossing the trail from Brute lake, S. W. % N. W. y sec. 18, T. 63-3 W., apparently in the 

 form of a dike. 



Ref. Annual Report, xxii, page 11. 



Meg. Apparently fine-grained, "pepper and salt" rock. 



Mic. The uugite is in large ophitic crystals embracing both olivine and feldspar, 

 while the olivine in a few instances gives place to the feldspar, and is also occa- 

 sionally altered to serpentine. One section. 



Age. Cabotian. N. H. w. 



