42 
HAYDEM : GEOLOGY OF SPITI. 
The thickness and extent of these beds overlying the Muth quaftz- 
Tu- 1 t ite is very variable. They occur in their fullest 
I hickness of car- ■' 
boniferous system very development in the section just described. In 
the Thanam valley they have been completely 
removed by permian or pre-permian denudation, but re-appear to 
some extent in Spiti, and at Muth in the Pin valley are represented by 
about 450 feet of siliceous limestone, calcareous sandstone and dark, 
Carboniferous at fossiliferous limestone. At about the middle of 
the series the limestone contains large numbers 
of Syringot hyris cusptdata, Mart., Spirifer sp., Dielasma sp. and 
Rhynchonella plenrodon, Phill., and 50 feet lower down a band was 
found almost entirely composed of Rhynchonella pleurodon. These 
beds almost certainly represent the fossiliferous limestones (No. 6) 
of the Lipak river, but the underlying beds which, in the latter locality, 
are about 1,000 feet thick must be represented at Muth by less than 
100 feet of limestone, calcareous sandstone and quartzite, and since the 
horizontal distance between Lio and Muth is only between 30 and 
40 miles, this must involve a remarkably rapid thinning out of the 
lower beds from east to west. 
To the north of Muih, at Kuling on the Pin river, the beds im- 
Carboniferous at mediately below the permian unconformity are 
Kuling. dark, flaggy limestones, apparently unfossiliferous, 
but underlain by a limestone very similar to horizon [a) of the Lipak 
section. The commonest fossils are — 
Productus cor a, d'Orb. 
„ semireticulatus, Mart. 
Rhynchonella pleurodon, Phill. 
Syringothyris cusptdata. Mart. 
With these occur also— 
Reticularia lineata, Mart., and Orthotetes (or Derbyia) sp. 
This band, which is seen just below the path from Kuling to Kungri, 
and again on the road from Kungri to Mikkim, is underlain by a thin 
bed of quartzite which passes down into hard limestones and quartzites 
overlying the Muth quartzite. 1 he beds below the fossiliferous lime- 
( 42 ) 
