24 HAYDEN GEOLOGY OF THE PROVINCES OF TSANG AND 0. 
of the Chorten Nyima La. The only fossils obtained by Professor 
Garwood were crinoid stems, which led him to identify these beds 
with the Tso Lhamo limestone described by Hooker* ; but since 
both of these occurrences have not as yet been visited by one and 
the same observer, their identity cannot be considered as definitely 
established, though undoubtedly probable. The Tso Lhamo limestone 
again bears an equally strong resemblance to a similarly small outcrop 
occurring among the Jurassic beds of the Phari plain near Agang ^ ; 
consequently, if all three are regarded as equivalent to one another 
the Lhonak limestone must also be of Jurassic age. The only objec- 
tion to this view is the appaxent position of that limestone with 
regard to the lower Jurassic beds of the Yaru plain, but the moraines 
on the northern slopes of the range may quite possibly hide one 
or more faults, and it is only by a visit to the Lhonak valley that 
the matter can be decided. 
For the present, therefore, the age of the rocks forming the range 
between Lhonak and Tibet must remain an open question, but in 
spite of some apparent evidence to the contrary I am inclined to 
think that it is in part Triassic. 
CHAPTER IV. 
THE JURASSIC SYSTEM. 
By far the most striking feature of the geology of southern Tibet 
is the enormous extent of the Jurassic system, which is exposed with 
little interruption over an area of many thousand square miles extend- 
ing from the northern flanks of the Himalaya to the Tsangpo — 
probably even to Nam Tso— and from the western boundaries of 
the Yaru plain to beyond Yamdrok Tso : to the west it probably 
• Himalayan Journals, II (1854), 177. 
* For further particulars see below, p. 26. 
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