[Sidenote: HOT SPRINGS. _September, 1847._]
As the day's journey was a very short one, we arrived at the salt plain by eight o'clock A.M. The air was still quite frosty. While our tents were being pitched on a dry bank a little way above the stream, we proceeded to its bank, and were not a little surprised to find the water quite tepid, notwithstanding the extreme cold of the air. On procuring a thermometer, it was found to have a temperature of 69°. Advancing up the stream, we found that numerous hot springs rose on its banks, and sometimes under the water. The hottest of these had a temperature of 174°. From these springs gas was copiously evolved, smelling strongly of sulphur; and in their immediate neighbourhood the water of the little river had a faintly sulphurous taste, though elsewhere it was quite pure and good. The stream, which was perhaps twenty feet wide, was usually rather deep. Dense masses of aquatic weeds, chiefly species of _Zannichellia_ and _Potamogeton_, grew in the water, and along the margins their dead stems, mixed with mud, formed immense banks, scarcely strong enough to bear the weight of a man, and yet seemingly quite solid. A small crustaceous animal was common among the weeds, but though I searched with care I could find no shells. The stream was full of fish, which swarmed among the weeds, and darted backwards and forwards in the tepid water in immense shoals. They were generally about six inches in length, and appeared to my inexperienced eye to belong to two or three species, all different from those which had been seen at Hanle. In the hottest water of the hot springs I collected three species of _Conferva_.
[Sidenote: MYRICARIA TREES. _September, 1847._]
The existence of the tree _Myricaria_ in the gorges between Pugha and the Indus, which had appeared to us at the time very remarkable, was fully explained by the occurrence of the hot springs, and the consequent high temperature of the water of the stream, and was peculiarly interesting as an illustration of the influence of temperature upon vegetation. It may fairly be considered, I think, as a proof, that arboreous vegetation does not cease at great elevations in consequence of the rarefaction of the air, but only on account of the diminution of temperature which usually accompanies increased elevation. The trees of _Myricaria_, it must be observed, came abruptly to an end with the ravine, none occurring on the open plain. We cannot suppose that the trifling increased elevation caused their disappearance; it seems probable that the narrow walls of the gorge, by concentrating the heat, prevented its escape, and that, therefore, the temperature was more elevated than in the open plain, where the action of winds and free radiation combined to lower it. The occurrence of fish in the water of Pugha, at an elevation of nearly 15,500 feet above the level of the sea, is also very remarkable, and still more strikingly demonstrative of the same fact, inasmuch as it would certainly not have been very surprising that air at that elevation should, from its rarity, be insufficient for the support of life in animals breathing by gills.