CAMBRIAN SYSTEM. I3 
The total thickness of the series cannot be even approximately 
determined, for although extending for many 
Thickness. 
miles in the valleys of the Thanam, Pin and 
Parahio rivers, with a more or less constant northerly dip, the beds 
have undergone repeated folding, and their apparent thickness is thus 
very great, especially in the Pin and Thanam valleys, where the 
arches of the anticlines have been completely removed by denudation. 
In the Parahio valley, however, remains of numerous folds can still be 
seen (see PI. I, fig. 2), thus proving that the enormous thickness is 
only apparent; it is probable, however, that an estimate of between 
two and three thousand feet will not err on the side of excess. 
The overlying beds which presumably comprise Mr. Griesbach's 
upper haimantas, consist of a series of black, 
Red and black slates. 
purple and grey slates, with grey, green, and red 
quartzites. The lower part of the series is chiefly argillaceous, and 
the upper mainly siliceous. The grey and purple slates are highly 
ferruginous, and contain large quantities of haematite and limonite, 
pseudomorphous after pyrite ; the weathered surfaces of the rock are 
consequently completely coated with orange and bright red films of 
ochre, and the outcrop stands out as a brilliant red band running 
through the darker slates, and presumably constituting Mr. Gries- 
bach's horizon of " red quartz shales." Among the argillaceous 
beds are bands of an intensely black, carbonaceous shale, resembling 
the carbonaceous shales of Simla. 
The red and black beds form an unmistakable and very constant 
horizon, well seen in the Parahio and upper Pin valleys of Spiti 
and the Thanam (locally called Samandar) river in Bashahr, where it 
has a thickness of not less than 1,000 feet. 
In the Parahio valley the upper siliceous beds pass up gradually 
Triiobite beds '"^'^ ^ series of grey and green micaceous quart- 
zites and thinly foliated slates and shales, with 
narrow bands of light-grey dolomite. 
The slates, which are usually dark-blue or black, vary in composition 
( 13 ) 
