From the pass the descent was considerably more abrupt than the ascent had been. The valley to the right was bare and stony, watered by a small streamlet, which had, as on the eastern face of the pass, cut a deep channel for itself among boulders. On descending, we turned gradually to the right, and a lake by degrees came in view, towards the southern extremity of which the road advanced over undulating hills of fine clay, full of fresh-water shells, almost entirely of one species of Lymnæa, of which the specimens were extremely numerous. This lake is the Thogji Chumo of Mr. Trebeck, who travelled along it on his journey from Le to Piti.
FOSSILIFEROUS CLAYS.
September, 1847.
I was much surprised, and not a little pleased, to find that the clay-beds contained fossils; as, except on one occasion in Piti, where I found one or two specimens of a small Planorbis, I had in vain sought in the clayey beds for any trace of organized beings. Here, however, shells were in prodigious abundance, and as the species was a large one, they were very conspicuous. The clay formation was horizontally stratified, and quite impalpable. The uppermost beds were at least a hundred feet above the level of the lake; and as the valley by which we descended was in its lower part almost horizontal, the lacustrine beds extended to a considerable distance from the lake, forming a slightly undulating surface, over which the road ran.
After reaching the banks of the lake, the road kept its eastern shore throughout its whole length, which was about three miles, and we encamped close to its north end, on the edge of a level salt plain. Our elevation was about 15,500 feet. The margins of the lake, which was intensely saline, were generally very shallow, and its banks often swampy, and covered with saline plants, especially Chenopodiaceæ; a species of Suæda, with cylindrical fleshy leaves, was especially abundant, growing in the soft mud close to the banks of the lake. A Blysmus, several grasses, and Ranunculus Cymbalaria were also common along the banks of the lake. No shells could be seen in the water. The surrounding hills were not very lofty, but often rose abruptly several hundred feet, and were in general rugged and rocky. At the height of perhaps 150 feet above the lake, a weathered mark could be traced on the face of the mountains, wherever they were rocky, everywhere quite horizontal. This was most conspicuous from a distance, and became indistinct on a near approach. It appeared to indicate, as I shall hereafter show, the level of the surface of the lake at some former period.
On the morning of the 25th of September, our day's journey commenced by rounding the north end of the lake, keeping at some distance from its margin to avoid swamp. For about two miles from the northern end, 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 north-west 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 Lymnæa.
ANCIENT WATER-MARK.
September, 1847.
FORMER OUTLET OF LAKE.
September, 1847.
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 Lymnææ 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 same ridge which we had crossed before descending to the salt lake. The axis of the range had been very near us on the right hand since we had crossed it on the 24th, and had sent down a succession of spurs, separated by wide valleys, along which we had been travelling. These separating ridges appeared usually to rise to an elevation of from one to two thousand feet above the nearly level valleys which lay at their bases, and were, though often rocky, less remarkably so than in many previous parts of our journey.
ASCENT TOWARDS TUNGLUNG PASS.
September, 1847.