CRYSTALLINE ROCKS. 23 



1). Interbodded with the gneiss, we occasionally find another gra- 

 nitic rock which is distinguished from the ordinary metamorphic granite 

 by being accompanied by a certain amount of local alteration and con- 

 tortion. Its strike is generally, if not always, coincident with that of 

 the adjoining metamorphic rocks j this feature separates it from true 

 igneous granite, which, although not met with in the area at present 

 under consideration, is found in several parts of the adjoining district 

 of Maunbhoom, where it cuts across, and is quite independent of the 

 strike of the surrounding rocks. 



The peculiar characters of this rock are probably due to the fact 

 that in age it was contemporaneous with the metamorphism, and that 

 it was either the metamorphosing agent itself or was directly connected 

 with it, and was thrust up and injected between the pre-existing beds, 

 which were then undergoing the process of alteration. 



The texture of this granite exhibits every degree of coarseness, and 

 is in no respect lithologically distinct from the other varieties ; in addi- 

 tion to the ordinary minerals, quartz, orthoclase (two varieties), and mica 

 (two varieties), it also contains hornblende and epidote, and less fre- 

 quently tourmaline and garnets. 



To this sub-division the proto^ine granite which is found in several 

 parts of the area seems to belong ; it consists of quartz, pink orthoclase, 

 and a green mineral allied to serpentine. 



c. The third variety traverses the gneiss and associated rocks 

 in directions which correspond to those of the principal joints or their 

 conjugates. It also occurs in places where there appears to have been 

 local crushing-up or contortion. 



As to what the origin of this variety may be, two alternatives 

 present themselves. On the one hand, it may be what is commonly 

 described as vein granite, and, on the other, its origin may resemble that 



( 131 ) 



