

CLASSIFICATION OF TUB ROCKS. 137 



possibly by superficial (subaerial) agencies. The picrolite is in all 

 probability the result of hydration of the olivine by subterranean 

 water accompanying the carbonic acid and included in the original 

 magma. This mineral may thus have been formed before, during or 

 after the formation of the magnesite, whilst the serpentinous product, 

 which has resulted from the action of subaerial agents, must have 

 been formed last and at the expense of the remaining portions of the 

 olivine. There is not, in my opinion, any evidence to show either 

 that the dunite suffered an early serpentinization, or that the magne- 

 site was formed by alteration of the serpentine. The two were 

 formed independently, and, on the whole, the magnesite, which is 

 the more abundant, was probably also the more early-formed of the 

 two. 



4c % — The " White Elephant rocks' \ 

 Two masses of white quartz are exposed on the southern 

 face of the Shevaroy hills, one on either side of the Gundur spur. 

 The eastern, which is the larger and most conspicuous, has been very 

 accurately described in the memoir by Messrs. King and Foote ; 

 its appearance is very well shown in the photograph reproduced in 

 plate II, which also shows the thick tangled nature of the jungle 

 surrounding the rock, and which makes it so difficult of access. 



The rock consists wholly of quartz, which is in coarse inter- 

 locking crystals, sometimes colourless and transparent, but generally 

 white through innumerable cavities containing a liquid which passes 

 into gas at about the critical temperature of carbonic acid. At the 

 ordinary temperature bubbles are always found in the cavities, the 

 very minute ones sometimes showing spontaneous movement. 



Messrs. King and Foote grouped these masses of quartz with 

 the younger acid intrusives, and the microscopic characters of the 

 crystals confirm their conclusion as to the eruptive origin of the 

 rocks. There are no signs of a clastic structure, such as we often 

 get in a quartzite, and no regular arrangement of the crystals as is 



( 35 ) 



