CAMBRIAN SYSTEM. I7 
Cambrian, and the overlying conglomerate adopted as the base of the 
Silurian system. 
This lithological break, with the accompanying unconformity, is 
constant throughout Spiti and Bashahr. The section above described 
is the most complete yet found, and the unconformity between the 
shales and quartzites (bed 18) and the overlying conglomerate (bed 
19), although distinct, is not pronounced, but a few miles further to 
the south, on the right side of the Parahio and in the high range 
between that river and the Pin valley, as also in the Thanam river in 
Bashahr, ample evidence of the break exists ; the conglomerate is found 
resting on a denuded surface o( the cambrian rocks, the greater part of 
the fossiliferous beds having in some instances been removed prior to 
its deposition. 
To the west and north the upper cambrian system is found chiefly 
in the great snowy range separating Spiti from the Kulu valley, and is 
to a large extent inaccessible, but wherever seen, similar denudation of 
the older rocks is found to have taken place before the deposition of 
the conglomerate. 
Even before the close of the cambrian period local disturbance 
^ ., , , , appears to have set in. Evidence of this is found 
Evidences of local 
disturbance during on the right bank of the Parahio, above Changnu 
upper Cambrian times. ^ , .1 ^ -i 1 -i. u • ^ j. 
'^'^ L. Cj., where the trilobite-bearmg slates are over- 
lain by the following series of beds : — 
19. Conglomerate. 
Unconformity. 
18. Dark siliceous and carbonaceous slates, 
17. Dolomitic limestone, passing horizontally into coarse conglomerate, 
16. Red siliceous shale, 
15. Dolomitic limestone, 
f Pink and red limestone. 
(, Grey limestone with shell remains. 
It will be seen that this section, which occurs at about a mile to the 
south-east of the river, corresponds to the section already described 
from the left bank, but between these two localities a striking change 
occurs in the upper limestone (No. 17) which passes horizontally into a 
great mass of coarse conglomeratCj composed of large blocks of the 
C 17 ) 
