the ground continued almost level, and contained great
masses of the lacustrine clay quite horizontally stratified,
and very little higher than the surface of the water, but
here quite without shells. A wide valley, rising gently
towards the north, lay beyond this level plain § but our
road, passing across the end of the lake, ascended another
valley, which ran in a north-west direction from its northwest
corner. The slope of this valley was very gentle. It
was bounded by low undulating or rocky hills, on which,
where the surface was suitable, the same remarkable
water-mark could be traced continuously, and still, to all
appearance, quite horizontal. The centre of the valley
was occupied by clay, at first non-fossiliferous, but a little
further on containing a great abundance of shells, the
same as in the bed seen the day before. A few specimens
of a very small bivalve, seemingly a species of Cyclas,
were also met with; but they were so very rare, that they
bore an infinitesimally small proportion to the Lymnaa.
For several miles the ancient water-mark could be
traced along the sides of the hills, appearing to descend
gradually, as the valley slightly rose in elevation. Beds
of clay continued to occupy the middle of the valley
nearly as long as the water-mark remained visible. At
last it disappeared where a depression on the left, leading
to the valley of Rukchin, seemed to indicate the
former drainage of the lake, at a time when its waters
occupied a much higher level, and contained in a living
state the large mollusca of which the shelly coverings
still remain in such vast abundance in the clay. As
it was at the very edge of the lacustrine clay formation
that the shells were so abundant, while the masses of
clay in the vicinity of our encampment of the 25th, at
the north-east extremity of the lake, were without any,
it would appear that the species was quite littoral, while
in the more central parts fine mud was deposited, without
shells. The outlet was indicated to me by Major
Cunningham, who in a previous journey had travelled
along a part of the Rukchin valley in descending from
the Lachalang pass towards the salt lake. As it may
fairly be inferred that the lake was quite fresh at the
time when it was inhabited by Lymncece and Cyclades,
it is satisfactory to know that so very small an increase
of the height of the surface of the water, as about 150
feet, would be sufficient to admit of its discharging its
waters along the course of an open valley into one of the
tributaries of the Zanskar river.
Our road, after passing the ravine on the left, along
which I suppose the discharge of the lake at its original
level to have been effected, turned still more towards the
north, and ascending an open valley to the right, crossed
a low col', or pass, and descended into a small basin surrounded
by hills, which was evidently at some former
period the bed of a small lake, for it was filled with pure
fine clay, in which, however, I could not observe any
shells. From this plain we passed into another open
valley, up which we ascended in a northerly direction for
five or six miles, encamping where the mountains on both
sides began to close in a circle. Throughout the day
we had been gradually but very gently ascending, and
the height of our encampment was probably about 16,500
feet. We were about two miles from the Tunglung
pass, a depression in the range parallel to the Indus, the