elxxxvi Proceedings of the Asiatic Society of Bengal. [N.S., XV, 
safe to say that the more volatile Sy will not be 
avis liquid as long as the temperature is above the critical 
point for water. Moreover, as long as the retcaiaes is at 
all high, there will be a tendency for a portion of the less 
volatile elements, such as silicon, aluminium, etc., to be kept 
in the vaporous condition by the help of fluorine, chlorine, 
boron, etc., which constituents are usually known as mineral- 
be w 
distance from the granite, in the nature of the substances 
eposited. 
In a complete case mica-bearing parma will be 
eposited in and next to the granite, 
Sequence of en 
in an ideal c 
SS a samarskite, columbite, and other rare-earth miner- 
The pegmatites pass upwards into aggregates of minerals 
di 
water—cassiterite, topaz, and tourmaline, being specially 
nhikrabbeatotie of this zone. Above the cassiterite zone should 
mingled, is also probably of pneumatolytic origin. Above this 
should come a zone of hydrothermal deposition ‘characterised 
by sulphide minerals such as those of copper, iron, lead and 
zinc, with gold and silver, of which the copper and iron 
sulphides tend to be depo sited nearest to the granite. Higher 
up still we may find penal quartz veins representing the 
surplus silica, and these may be succeeded by hot springs 
representing the final surplus of water. 
This is, of course, the simple and ideal case pieced together 
from the evidence of many localities in different parts of 
the world. In practice, in any given case, some of the zones of 
deposition may be missing ; in addition, as the general tempera- 
ture decreases, each zone may r recede towards the granite, 
so that, e.g., ae characteristic of the hydro-thermal zone 
superposed on those of the pneumatolytic zone of 
a nag aw earlier eel of deposition 
e following study of ore deposition in Singhbhum, 
Sikkim ahd Mysore, we shall in each case find it reasonable 
to attribute to intrusions of acid igneous magmas the intro- 
