208 TRANSACTIONS OF THE [APR, 24 



deformation in the bending and breaking of twinning lamellse 

 and very marked undulatory extinction. 



The i^yroxene is colorless or pale green, with extinction angle 

 of about 45°. There is a certain amount of alteration to 

 chlorite, but the most noticeable change is the passage into dark 

 green uralite. The uralite, as a rule, makes up onl}' a small 

 part of the individual, but in a few cases has replaced most oj 

 the pyroxene. Besides the uralite there is present a s-mall 

 amount of hornblende, which seems to be original. 



Biotite is present in large quantities, partly in large plates, 

 and partly in small scales of secondary origin. 



The relation of the dark band to the surrounding rock is 

 such that it must be regarded as belonging to the gneiss just as 

 much as the other dark bands ; and yet from its mineralogical 

 composition there can be little doubt that it is intrusive. The 

 same explanation must apply to many of the dark bands, though 

 it is not often so clearlj- indicated. 



GRANITE. 



There is evidence of a long time break between the gneiss 

 and the granite, with corresponding structural differences ; but 

 in mineralogical composition there is considerable similarity' 

 between the two rocks, the most marked difference being the 

 greater amount of plagioclase in the gneiss. 



The granite is usually of a light gray color, and of rather 

 coarse grain, but there are many wide variations from this 

 general type. Similar variations occur in its mineralogical 

 composition ; the rock being, as a rule, a biotite granite, or 

 granitite, but showing many local transitions into pegmatite, 

 tourmaline granite, hornblende granite, diorite, etc. 



The quartz of the granite is either clear white and colorless, 

 or milky, the latter appearance being due to the presence of 

 abundant fluid inclusions. The microscope shows, in many 

 instances, besides these fluid inclusions, slender, black, hair-like 

 bodies usually regarded as rutile. These vary considerably in 

 number, size and arrangement. In some sections they are scat- 

 tered quite irregularly through the quartz, while in others they 

 show a tendency towards parallelism. In a single case the hairs 

 form two distinct groups. The first consists of quite short bodies 

 scattered very irregularly through the quartz. The second 

 group consists of unusually long hairs, so arranged as to form 

 a network with square meshes. The hairs of the net are more 

 abundant iu one direction than the other, the most numerous 



