i8 
HAYDEN: GEOLOGY OF SPITl. 
same limestone in a calcareous matrix. Mixed with the limestone 
blocks are a few pebbles and angular fragments of quartzite, resem- 
bling that of the underlying beds. The conglomerate occurs on both 
sides of the river, but is particularly well seen above the right bank, 
where it forms a cliff above 250 feet in height, but rapidly dwindles 
away on either side and passes horizontally into the normal dolomite. 
The main mass of the conglomerate consists of very large blocks, 
often as much as a ton in weight, of the grey limestone and of the 
dolomite found in the adjacent sections, but near the base of the 
cliflf it is composed of large boulders — many being of quartzite — from 
six inches to a foot in diameter, embedded in a siliceous and slaty 
matrix. This rests on an eroded surface of upper cambrian slates 
and quartzites (PI. VI). It would appear, therefore, that towards 
the close of the cambrian period disturbances had begun to take 
place locally, resulting in contemporaneous erosion. The original 
conditions, however, seem to have been soon restored, for both the 
conglomerate and the dolomite are overlain by the same band of dark 
slates (No. 18), above which occurs the great cambro-silurian uncon- 
formity, which extends throughout Spiti and Bashahr. 
No further evidence of local disturbance during upper cambrian 
Cambro-silurian times has been observed, for the highest beds 
unconformity. of that system have been found only in the 
Parahio valley. Thus, on the high range to the west of Muth in the 
Pin valley and a few miles south-east of the Parahio, the lower silurian 
conglomerate rests in places on a small thickness of the lower dolomite 
(bed 15), and in places on the underlying slates, while on the lower 
spurs on either side of the Pin river, the dolomite has completely 
disappeared and only the lower beds of the upper and middle cam- 
brian are found. Higher up the river also, near Baldar, the upper 
beds are entirely absent. 
Still further to the east, in the valley of the Thanam river, near 
the junction of that river with the Chokdinjan Chu, the greater part 
of the upper and middle cambrian series has been removed. No 
trace is seen of the dolomite, the conglomerate being underlain 
( 18 ) 
