IGNROUS ROCKS. 
97 
Chapter vn. 
IGNEOUS ROCKS. 
The high ranges bordering Spiti on the south, west and east are 
as has already been stated, composed chiefly of granite ; basic intru- 
sions occur among the palaeozoic beds of lower Spiti and Bashahr and 
in the valleys of the Parahio and Pin rivers. 
Granite. 
The commonest form of this rock is a biotite granite, ranging from 
• . a fresh rock of medium grain to a foliated gneiss- 
loti e gran 13 variety with large porphyritic felspars. In 
the Sutlej valley, near Asrang and Jangi, numerous masses occur in 
the altered cambrian slates. The rock is here very pure and free from 
accessory minerals, consisting mainly of quartz, orthoclase and biotite, 
with a little muscovite and plagioclase. 
Associated with the biotite granite in the Sutlej valley, in the 
Chandra valley, and in the ranges between Kulu 
Pegmatite. . , ^ . . 
and Spiti, are numerous vems of albite granite, 
containing large quantities of schorl, muscovite, beryl and, locally, 
garnet and kyanite. Both these types have been previously described 
by General McMahon and other observers and no further .details need 
be given in the present memoir. 
1 he Rupshn granite is very similar in general characters to that 
of the Sutlej and Chandra valleys, being a biotite 
Rupsha granite. . ., , 
granite with few accessory minerals ; it differs 
slightly, however, in containing — as at Dongan Le, where it is accom- 
panied by eurite — a considerable amount of blue quartz. In spite of this 
difference it is almost certainly merely an offshoot of the Sutlej valley 
massif, for it can be traced up to the southern boundary of Rupshu and 
can be seen running through the high range which borders the eastern 
side of the P4ra river above Akse and Kharak in Western Tibet, and, 
were it possible to follow it through that country, it would probably be 
H ( 97 ) 
