34 HAYDEN: GEOLOGY OF THE PROVINCES OF TSANG AND 0. 
The lower beds are characterised by the presence of large numbers 
of lamellibranchs, of which Trigonia costata is especially noticeable, 
occurring in great quantity in an arenaceous band about 20 feet 
above the base of the limestone. 
Brachiopods are apparently absent from the lowest beds and are 
especially characteristic of the middle of the series, while the cephalo- 
pods (ammonites, nautili and belemnites) were found only in the 
highest beds. 
Although it has so far been possible to determine only a few 
of the Lungma fossils, there is little doubt that they should 
be referred to the Inferior Oolite of Europe. Unfortunately this 
fossiliferous series has not been definitely recognised in any 
other locality, although the E.-W. strike would lead one to expect to 
find it elsewhere along the southern edge of the Yarn plain, but, owing 
partly to faults and partly to extensive talus fans and moraines, no 
other outcrops were found in the area examined : probably, however, 
it reappears in the hills to the west of the Yaru plain which form the 
boundary between Tibet and Nepal, and which, owing to political 
considerations, were not accessible. 
The lower slates exposed on the ridge^ at the foot of the ascent to 
the Naku La contain a few traces of fossils, including a small 
Pecten sp. 
The slates and shales which overlie the limestone also contain 
traces of fossils, but nothing determinable was found in the beds 
between the Lungma section and the Spiti shales near Kampa 
dzong. Even in the latter the fossils are scarce and very badly pre- 
served and not comparable to those found in the more westerly sections 
of Garhwal and Spiti. 
With the exception of the Cretaceous series of the Kampa ridge no 
system other than the Jurassic is represented in any part of the Yaru 
plain visited : and, as elsewhere in Southern Tibet, the great extent 
of this system is most remarkable. 
'The pass crossing this ridge is Itnown as the Sokar La. 
( 155 ) 
