THE JURASSIC SYSTEM. 
35 
Synthesis of Jurassic system. 
Before passing on to the rest of the area traversed during the 
recent expedition, it will be advisable to summarise the results of the 
examination of the exposures described above and, so far as possible, 
piece together the disjointed parts into one consecutive whole : this 
is rendered particularly difficult by the isolated character of the 
exposures, which can so rarely be traced from one locality to another, 
partly on account of faulting, which, in spite of the gentle dip of many 
of the beds of the Yaru plain, is nevertheless very considerable in 
places, as along the Giri river and again in the hills behind Kampa 
dzong ; partly also owing to the extensive moraines and talus slopes 
which, except near Lungma, obscure all the older beds. Fortunately 
the section from the slates below the Lungma limestone is fairly 
continuous up to the Spiti shales, and we have thus two known 
horizons on which to base a synthesis of a considerable part of the 
system : but between the limestone with Trigonia costata and the 
Spiti shales no determinable fossils have been found, and we are thus 
compelled to group the intervening beds into a single series 
presumably comprising all the intermediate stages, that is to say 
the remainder of the middle, and all except the uppermost, Jurassic. 
With the lower beds it is more difficult to deal : those underlying 
the Lungma limestone are probably continuous with the slates and 
quartzites of the Kongra La, while the Tso Lhamo limestone is 
almost certainly older than these. 
The Jurassic series of the Lachen-Kampa dzong area n ay there- 
fore be tentatively classified as follows : — 
Spiti shales .... 
Black and grey shale and quartzite 
Lungma limestone . 
Slate, quartzite and conglomerate . 
Tso Lhamo limestone . 
O 2 
. Upper Jurassic. 
C Partly upper i 
. < { Jurassic. 
(, „ middle ) 
. Middle Jurassic. 
* j Lias. 
( ) 
