62 HAYDEN: GEOLOGY OF THE PROVINCES OF TSANG AND U. 
There would thus appear to be three series of igneous rocks in- 
Central Tibet, viz., {a) the foliated biotite granite of the Himalaya, 
with its associated schorl granite, {b) a series of basic dykes chiefly 
diabase and serpentine, and (c) the hornblende-sphene granite and 
associated hornblende-diorite, of the Tsangpo and Kyi Chu valleys. 
The first of these series is undoubtedly merely a continuation of 
the great granitic axis of the Himdlaya ; it is intrusive certainly into 
beds of Jurassic age, and to the north-east of Chomolhari, in the neigh- 
bourhood of the Lingshi La, will most probably be found to have aflfected 
the Cretaceous and Tertiary beds of the Kampa series, in which 
case it could not be older than eocene. This has not been definitely 
ascertained, but unless the Lingshi range proves to be an original 
limit of deposition — a rather improbable supposition — it is impossible 
to avoid the conclusion that the Kampa series is represented among 
the metamorphosed sediments in the peaks to the north of the 
Lingshi La. This particular area has not been visited, but its impor- 
tance is apparent since, should the Kampa series be found there, it 
will furnish the first positive evidence of the Tertiary age of the 
Himalayan granite. 
Since the basic volcanic series of Ladak and Kumaon^ are regarded 
as of eocene age, the dykes found intrusive in them in both areas 
are therefore either practically contemporaneous or probably younger. 
Similar rocks have also been found intrusive in the biotite-granite of 
Rupshu,^ and if we are justified in assuming that the diabases and 
serpentines of Central Tibet are but part of the same series, they also 
must be younger than the biotite granite.' 
There is still less direct evidence, with regard to the age of the third 
series, the Kyi Chu granite and associated hornblende-diorite. It 
' R. Lydekker : Mevi. Geol. Surv. Ind., XXII, ni ; A. von Krafit : Mem. 
Geol. Surv. Ind.,XXXU, 138. 
2 H. H. Hayden : Mem. Geol. Surv. Ind., XXXVI, loo. 
' We are unfortunately dependent on this indirect and somewhat involved, 
method of argument in endeavouring to fix the age of the basic intrusive rocks of 
Central Tibet, since they were not observed in contact with granite in the compara- 
tively limited area that could be visited. 
( '83 ) 
