THE JURASSIC SYSTEM. 
29 
This small patch of rock is quite isolated and crops out from 
among masses of talus and old moraine material. The nearest rocks 
found in situ are the altered beds of the DrongkhyaLa and a series of 
more or less altered slates, shale and quartzite forming a small group 
of hills on the opposite side of the lake and belonging to the 
series of Jurassic beds which extend from the Kongra La to Kampa 
dzong. The outcrop consists of black shale overlain by beds of 
shale and flaggy sandstone, followed by the supposed "nummulitic" 
limestone which is in turn overlain by hard dark limestone with 
crinoid stems ; these have been altered into white crystalline calcite 
and consequently show no structural details. All the beds dip at 
moderately high angles to the north (see PI. 3, fig. i). 
No similar rocks have been observed anywhere in the neighbour- 
hood, but in the range of hills on which Kampa dzong stands a 
bed occurs high up in the Cretaceous system, which, in macroscopic 
characters, is apparently identical with the " nummulitic " limestone 
of Tso Lhamo ; so great is the similarity of the two that the Tso 
Lhamo rock was unhesitatingly referred by me to the Cretaceous 
system, in spite of its anomalous position, many miles from other 
Cretaceous rocks and apparently among the lower beds of the 
Jurassic system. The Cretaceous rock referred to also resembles 
nummulitic limestone, but is in reality composed of Orbitoides sp. 
which occur as dark circular and ovoid patches in a bluish grey 
matrix. In the field therefore the Tso Lhamo rock was referred to 
the Orbitoides limestone, and it was only by means of the microscope 
that its true character was discerned. Instead of the beautiful 
structure shown by the foraminifera of the Cretaceous rock, the 
ovoid patches of the Tso Lhamo limestone proved to be chiefly oolitic 
grains and showed no trace of foraminifera. No grounds therefore 
exist for referring this rock either to the Cretaceous or Tertiary 
system, and since the only beds exposed anywhere near it are 
Jurassic slates it seems more natural to refer it to that system, and to 
correlate the crinoid limestone of Tso Lhamo with that of Agang 
in the Phari plain. In addition to the crinoid stems a few very 
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