PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 207 



Basalt.] 



probable that the rock here described represents a spherulitic glass, although the 

 circular areas may possibly be gas cavities rather than old spheruliths. 



One section. 



A(/f. Cabotiau; red-rock series. u. s. G. 



No. 136. BASALT (with acid inclusions}. 



Opposite the fifth island oast of Beaver bay. 



Ref. Annual Report, ix, page 34; Annual Report, x, page 141; Bulletin ii, page 125; American Association 

 for the Advancement of Science, vol. xxx, page 164. 



Ma/. A medium-grained, brown-green rock, with much quartz. The brown or 

 brownish-red color is produced by a stain of the feldspathic ingredient. The green 

 is confined to an amorphous green substance which is abundantly disseminated 

 through the rock. The quartz is disseminated micro-pegmatitically amongst the feld- 

 spars and also occurs in the green substance. The feldspars are not wholly stained 

 red, but the central portions are frequently white. They seem to be frequently 

 twinned on the Carlsbad plan and occasionally the albite striation can be seen. 

 There is also a considerable amount of amorphous red substance which cannot be 

 called feldspar, though probably feldspathic. 



Mic. The feldspars are permeated with impurities. They are largely or wholly 

 of the plagioclase family, some of them being minutely twinned on the albite plan; 

 yet, in some parts of the slide, they can hardly be separated from the reddish amor- 

 phous substance throughout which quartz is intergrown pegmatitically. 



Qiirniz has a single orientation, sometimes, over considerable areas which also 

 enclose portions of the amorphous green and red substances, as well as what appear 

 to be altered phenocrysts of feldspar. It also ramifies in a branching and spreading 

 manner through some of the feldspars having, in that case also, a single orientation. 

 It is thus evident that it is of later date than any of these substances. 



The red feldspathic substance is easily recognizable as that which makes up the 

 largest part of the "red rocks" of the region. It gave rise to orthoclastic feldspars 

 when it was allowed to cool slowly, and it may be the generator of the most of the 

 Carlsbad twinned crystals in this section. At least it may be stated that it has a 

 close alliance with the reddened feldspars of this rock, for sometimes it seems to pass 

 insensibly into the crystalline feldspathic condition. 



The green amorphous substance, in a like manner, shows evidence of having 

 been the magma of a basic rock. It is the same that is seen in No. 133, but is here 

 more abundant. It surrounds the feldspars, and sometimes small portions of it are 

 included in them. It solidified later than they. It is now in the form of a chloritic 

 mineral (pennine?), and occasionally it is cut favorably for showing its pleochroism. 

 Magnetite appears in distinct masses, and hematite is everywhere as a coloring 

 substance. 



