About two miles west of Tarkata, the Indus resumes its more usual direction, and, at the same time, its valley becomes somewhat more open, the mountains, without any diminution of elevation, receding considerably from the river. Their lower slopes present a very different aspect from those in other parts of the Indus, being composed not of primitive rock, but of a soft and almost incoherent sandstone, alternating irregularly and without any definite order with boulder conglomerate, and fine clay. These beds, which are very extensively developed on both sides of the river, around the village of Tarkata, for some distance in both directions, attain a thickness of at least six or seven hundred feet. They are, however, very irregular, forming a succession of ridges separated by deep ravines or gullies, on the sides of which fine sections of the strata are generally exposed, showing them to be uniformly horizontal, and to consist of a great many alternations of sand, clay, and drift. Above Tarkata, very fine clays were abundant.
[Sidenote: SOFT SANDSTONE ROCKS. _December, 1847._]
The sandstone, of which a greater part of these curious deposits consists, is formed principally of coarse grains of quartz, which only cohere very slightly, and easily crumble under pressure. It is quite similar in appearance to the sandstone which occurs on the summit of the rock of Iskardo, differing only in being very much more extensively developed than that is, and in being associated and alternating with the very fine clays resembling those which occupy the lower levels of the valley of Iskardo. The sandstones of Tarkata did not appear to be fossiliferous, nor did I, in the slight examination I was able to give them, discover any shells in the fine clays in this neighbourhood. The general similarity, however, of these deposits to the lacustrine clays of the Iskardo valley, makes it nearly certain that their origin is similar, while the association of the sandstones and the fine clays in the neighbourhood of Tarkata, renders it probable that I am right in assuming the arenaceous beds of the summit of the rock of Iskardo to be lacustrine.
[Sidenote: FLOATING ICE. _December, 1847._]
Ever since leaving Iskardo, the weather had been very unsettled, but no more snow had fallen. The sky had been pretty generally overcast with light clouds, and during the day the wind had almost invariably blown down the river, generally with great violence, and, especially in the narrowest parts of the valley, in furious gusts, against which it was most laborious to make any progress. The mornings had been always frosty, but the temperature rose in the middle of the day several degrees above 32°. On the 8th of December, a sudden increase of cold seemed to take place, the temperature not rising above the freezing-point. Large cakes of ice, which appeared early on the morning of that day, floating down the river, indicated an evident commencement of very severe weather in the upper part of its course, and the descent of such masses of ice, in cakes of from one to ten feet in diameter, tended very much to lower the temperature of all parts of the river to which they extended. The elevation of Tarkata I found to be 7800 feet above the sea.