94 
HAYDEN : GEOLOGY OF SPITI. 
Between Narbo Sumdo and the northern end of Tso Moriri the 
Representatives of whole of this palaeozoic series can be traced, the 
palaeozoic systems. calcareous schists, conglomerates and quartzites 
of the permian being underlain by the altered representatives of the 
rest of the Po series of Spiti. A little to the south of Korzok, the 
siliceous beds are underlain by calc-schists and crystalline limestone, 
as already recorded by Mr. Oldham.^ From Korzok a small ridge 
runs to the northern end of the lake ; this ridge consists of calc-schist 
and crystalline limestone with some bands of white quartzite, the 
whole similar, except in the somewhat smaller thickness of the quart- 
zite, to the section seen at Shalshdl Dengo. These beds have, there- 
fore, been referred also to the carboniferous, but it is possible that 
they may be also partly silurian. 
The limestones and quartzites are underlain by slates and schists 
which gradually become garnetiferous, then felspathic, and pass down 
into the so-called " Tso Moriri gneiss." 
This rock was cursorily examined by the present writer in 1899,. 
and on account of its apparent position among 
Tso Moriri gneiss. .... .,01. 
the palaeozoic beds it was suggested that it 
might possibly be a highly metamorphosed representative of the 
lower silurian quartzite of Spiti. Subsequent determination of the 
microscopic and chemical characters of the rock, however, showed 
that there was no evidence in favour of regarding it as primarily of 
sedimentary origin. 
As already stated by Oldham {loc. cit.), it forms an apparently 
well-bedded series, with foliation parallel to bedding, the beds 
being about two feet thick. In uiineralogical composition, it is 
chiefly an augen gneiss, with large "eyes " of felspar. Most of the 
beds are composed of a quartz-felspar-mica rock, with rods of 
schorl on the foliation planes. The quartz frequently occurs as a 
mosaic of small grains. The felspar is chiefly orthoclase and micro- 
cline with a little plagioclase, w hile the mica is a pale, often colourless 
» Records, G. S. I., vol. XXI, p. 153. 
* General Report, G. S. I., 1899-1900, p. 197. 
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