58 HAYDEN: GEOLOGY OF THE PROVINCES OF TSANG AND 0. 
an ophitic augite-norite and is very similar to other dyke-rocks found 
between Hring La and Nangkartse and along the shores of Yamdrok 
Tso. There is nothing sufficiently remarkable about the rock to 
warrant a detailed description : it is composed of plagioclase, probably 
labradorite but much decomposed, augite and enstatite both markedly 
ophitic, chlorite serpentine, probably derived from the decomposition 
of the pyroxenes, ilmenite, leucoxene and sphene. 
At the village of Nupuchondzo between Drongtse and Penang 
there is a very conspicuous intrusion of serpentine with large 
lustrous phenocrysts of bastite. It has been considerably crushed 
and the black and shining slickensided surfaces give it a superficial 
resemblance to coal, which probably accounts for the persistent 
rumours regarding the occurrence of that mineral between Gyantse 
and Shigatse. 
All the above rocks are found intrusive in the Jurassic slates, but 
a dyke of similar character was also noticed among the limestones, 
regarded as of Cretaceous age, between Trolung and Nyetang in 
the valley of the Kyi Chu. They are therefore not older than 
upper Cretaceous and may be younger, possibly contemporaneous 
with the basic intrusions which are found in the Tertiary volcanic 
series of Ladak- and in the Palaeozoic beds of Spiti and Rupshu, and 
it further seems reasonable to unite these occurrences of basic 
igneous rocks, as well as the dacites of the Tsangpo gravels, with the 
volcanic series of Malla Johar in Kumaon* and the neighbourhood of 
Manasarowar and Rakas Tal° and to regard them all as Tertiary (later 
eocene) in age. 
The most constant feature of the rocks described above is their 
' Fragments of similar basic rocks related to diabase and epidiorite were also 
found in the Kampa dzong and Phari areas ; they were not seen in situ but are 
presumably intrusive in the Jurassic slates. 
5 Petrological notes on some Peridotites, elc, from Ladakh ; by l.t.-Genl. 
C. A. McMahon, F.R.S., Mem. Geol. Surv. Ind., XXXI, pt. 3. 
3 H. H. Hayden : Mem. Geol. Surv. Ind., XXXVI, pt. I, 98. 
* A. von Krafft : Mem. Geol. Surv. Ind., XXXII, pt. 3. 
• R. Strachey : Journ., R. Geol. Surv. Soc, XXI, 1851 ^68) ; Q. J. G. S., VII 
(1851), 308. 
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