THE JURASSIC SYSTEM. 
25 
extends more or less continuously along the northern frontier of 
Nepal to Ngari Khorsum, while on the east nothing is known of the 
country beyond Yamdrok Tso, but it is not improbable that the 
Jurassic beds will be found to extend to the N.-S. bend of the Tsangpo 
or even beyond this to the flanks of the great meridional mountain 
ranges of eastern Tibet. 
The general lithological characters of the system are not unlike 
those prevailing in other parts of the Himalaya, In both cases the 
upper beds are wholly free from limestone, but whereas in the 
western areas the lower and middle Jurassic rocks are entirely 
calcareous, in the east they are only partially so, and even among 
the lower beds sandstone and shale are the predominant types. 
Except in the Phari plain, their southern boundary is formed by 
the granite of the crystalline zone, but since the junction runs along 
the slopes of the granite hills, it is usually obscured by talus or 
moraines; near Gyaugang, however, and on the Kongra La the 
slates appear to pass through schistose and gneissose rocks into the 
foliated granite. Not only are the lower beds metamorphosed but 
they are also considerably disturbed, and owing to the further 
complications introduced by the numerous moraines, observations 
along the northern frontier of Sikkim could be made only on 
disconnected patches, which, however, when taken in conjunction 
with other occurrences near Kampa dzong and in the Phari plain 
can be correlated with sufficient approximation to certainty to furnish 
a fairly complete s)'nthesis of a considerable part of the system. 
The most convenient method of treating these isolated occur- 
fences, will be to describe each in detail, and then attempt to 
correlate them with one another. 
For this purpose the most important localities are : — 
a. A gang in the Phari plain. 
b. Tso Lhamo. 
c. Kongra La. 
d. Naku La to Kampa dzong. 
( 146 ) 
