WHITE: PETROGRAPHY OF THE BOSTON BASIN. 
131 
crystals and the interference of the polarization colors of the usually 
inclosing feldspar. These results determined the needles to he 
glaucophane, and it is interesting to note that the same conclusion 
was reached by Dr. M. E. Wadsworth (’83, No. 71), although no 
mention elsewhere has been made of the abundant occurrence of 
this interesting mineral in the Quincy granite. 
The hornblende granite of Geising in Saxony is very similar in both 
macroscopic and microscopic appearance, although the hornblendic 
needles are shorter. It also resembles the granite of Mts. Adam 
and Eve, Orange Co., N. Y. (Kemp and Ilollick, ’94, p. 641), but 
the latter has more quartz. In the Orange County locality the 
rock is said occasionally to approach quartz porphyry in texture. 
The feldspar is mostly much strained and broken. 
Quartz varies from colorless to the smoky variety and is very 
closely mixed with the feldspar, although less plentiful. Hair-like 
needles, too minute for determination, are occasionally met with in 
the quartz. 
Biotite occurs sparingly as brown Hakes scattered through both 
quartz and feldspar. 1 
In portions of the granite local segregations of various mineral¬ 
izers occur in small quantity. These are especially noticed in the 
neighborhood of contacts. Fluorite is thus found in beautiful, 
bluish purple, partly crystallized masses of microscopic dimensions, 
intermingled with altered pyroxene. Aegirine occurs sparingly, in 
long, bright green shreds. Zircon forms doubly terminated crystals. 
Danalite has been reported by Dr. Wadsworth (’78, p. 310), but 
Dr. Wadsworth, to whom I am indebted for a cordial response to 
inquiries, writes that the mineral was reported from field observa¬ 
tions and not from thin sections. 
In many places, notably at the small quarry on Rattlesnake Hill, 
segregated patches of darker color are observable in the granite. 
These vary in size from a few inches up to several feet in diameter, 
and are usually roughly oval in form. They are of a dark bluish 
gray color, are much finer grained than the remainder of the 
rock, and are formed by concentration of the dark silicates, very 
much in the same way as the diorite of type 1, above. In most cases it 
shows more conspicuous quartz, in rounded grains of larger size 
than the other minerals, either white or smoky. It is accompanied 
1 Cooke (’67, p. 222) lias shown the black mica of the Cape Ann granites to be lepido- 
melane. 
