in the valley, nor on the slopes on either side. Elevation
could not be the cause of this, the height being
much lower than the line of upper limit of tree vegetation
in the outer Himalaya, and the temperature of the
valley, as was evident from the kinds of grain cultivated,
very much greater than it would have been at the same
level, in the more rainy climates nearer the plains of India.
The ravine through which the Lio stream runs is narrow
and rocky, and, contains a great number of transported
blocks of various sizes, scattered irregularly over
the surface. Close to the village there is a curious isolated
rock, separated by the stream from the mountain
mass with which it has evidently once been connected.
On the 25th of August we crossed the Piti river, a
little above Lio, and ascended to the village of Nako,
on a very steep ridge, which descended from the great
mountain Porgyul. After leaving the cultivated lands
of Lio, which extend for half a mile from the upper
part of the village, we ascended the right bank of the
Piti river for nearly a mile, to a bridge, by which it is
crossed. The river ran here in an extremely narrow
ravine, precipitous mountains rising on either side.
Its banks were steep, and covered with loose shingle,
the débris of the precipices above. The stream is
of considerable size, but much inferior to the Sutlej
where we had last observed it close at hand, though
I believe it is nearly as large as that river, at the point
of junction of the two. The Piti runs in this part of
its course with great rapidity, and is probably of considerable
depth.
The bridge was situated at a bend of the river, where
the rocky banks contract more than usual. It was
s imila r in structure to that over the Sutlej at Wangtu,
but much smaller, and in so dilapidated a state, that it
could scarcely be expected to last another year. The
ascent to Nako was throughout steep, the difference
of elevation being about 2500 feet, and the distance
not more than two miles and a half. When at a sufficient
height above the narrow dell in which the Piti
runs, a good view was obtained of the mountains by
which we were surrounded, which rose on all sides in
rugged precipices. The steepness of the cliffs allowed
their geological structure to be well seen. The fundamental
rock, wherever I saw it, appeared to be clay-
slate, sometimes passing into chert or quartzy sandstone^
This basal rock was everywhere traversed by
innumerable veins of quartz and granite, which exhibited
no signs of parallelism, but ramified in every direction.
These veins were often of great thickness. Not unfre-
quently, indeed, the mass of granite much exceeded the
slaty beds between which it was interposed; but its connection
with other veins of more moderate size rendered
it evident that it had been injected into the slate.
Behind the village of Lio a thick deposit of alluvial
clay was discernible, which seemed to suggest the idea
of the valley having formerly been a lake; and at no place
where I had seen these clayey accumulations was this
hypothesis so plausible, for the precipices south of the
junction of the Lio stream, rose almost perpendicularly
for more than 1000 feet above the Piti river, and approached
so close to one another, that their disruption
was at least a possible contingency.