RUPSHU. 
95 
and silvery, magnesia mica. In hand specimens it resembles musco- 
vite, but under the microscope appears to be perfectly uniaxial, while 
chemical analysis shows it to contain a large amount of magnesia: it 
must therefore be classed under biotite. 
With this gneiss are associated bands of white quartz-felspar-mus- 
covite rock, containing no biotite, but with a considerable amount of 
plagioclase and some schorl. Low down in the series, near Shakshang 
E. G., fine-grained quartz-biotite schist is found interbanded with the 
gneiss. It is composed of large quantities of dark brown biotite and 
finely granular quartz ; with it occur also bands of a similar rock, 
but considerable quantities of zoisite and calcite are added to the 
ether constituents; these two schists have many of the characters of 
altered sedimentary rocks. 
Running through the above series, in bands usually parallel to, but 
Intrusive biotite occasionally crossing, their foliation, is another 
granite. quartz-felspar-biotite rock, foliated and gneiss- 
ose, but containing biotite in irregular blotches and not in layers 
as in the " Tso Moriri gneiss." It has hitherto been included with 
the latter rock, but is almost certainly younger and intrusive in it. 
The same rock occurs again at Ooti E. G., about 40 miles further to 
the south-west, where it forms a broad, apparently gneissose, band in 
the middle of the metamorphic schists which represent tlie carboni- 
ferous and permian beds of Spiti. No signs of the augen gneiss of 
Tso Moriri are to be seen at Ooti. The true origin of this rock can 
only be ascertained by much more detailed work than has hitherto 
been possible, and must for the present remain doubtful, but the 
evidence so far obtained tends to show that it is a foliated biotite 
granite ; whether it is identical or not with the common biotite granite 
of Rupshu is also uncertain, but it is much more foliated and may 
belong to an older series of intrusions. 
Even more doubtful is the age and origin of the Tso Moriri 
Age and origin of gneiss ; by Lydekker it was regarded as archaean, 
Tso Monri gneiss. ^ut its position, underlying rocks which are not 
older than silurian, and the gradual lithological passage from the 
( 95 ) 
