GEOLOGY. 275 



which was apparently about 3,000 feet above me. All the rivers had 

 formed for themselves depressions in the platform of gravel which 

 was spread over the plain. I ascended this valley for about six miles : 

 its width varied from 200 yards to about half a mile, gradually 

 widening as I ascended. The slope was throughout gentle. An 

 accumulation of alluvium frequently formed broad and gently-sloping 

 banks, which were cut into cliffs by the river. Now and then large 

 tracts covered with glacial boulders were passed over ; and several 

 small streams were crossed, descending from the northern mountains 

 through narrow ravines. About eight miles from my starting-point 

 the road left the bank of the stream, and began to ascend obliquely 

 and gradually on the sides of the hills. The course of the valley 

 beyond where I left it continued unaltered, sloping gently up to a 

 large snow-bed, which covered the side of a long sloping ridge four 

 or five miles off. After a mile, I turned suddenly to the right, and, 

 ascending very steeply over fragments of rock for four or five 

 hundred yards, I found myself on the top of the Karakorani pass 

 a rounded ridge connecting two hills which rose somewhat abruptly 

 to the height of perhaps 1,000 feet above me. The height of the pass 

 was 18,200 feet, the boiling point of water being 180.8, and the 

 temperature of the air about 50. Towards the north, much to my 

 disappointment, there was no distant view. On that side the descent 

 was steep for about 500 yards, beyond which distance a small streamlet 

 occupied the middle of a very gently sloping valley, which curved 

 gradually to the left, and disappeared behind a stony ridge at the 

 distance of half a mile. The hills opposite to me were very abrupt, 

 and rose a little higher than the pass ; they were quite without snow, 

 nor was there any on the pass itself, though large patches lay on the 

 shoulder of the hill to the right. To the south, on the opposite side 

 of the valley which I had ascended, the mountains, which were 

 sufficiently high to exclude entirely all view of the lofty snowy moun- 

 tain seen the day before, were round-topped and covered with snow. 

 Vegetation was entirely wanting on the top of the pass, but the loose 

 shingle with which it was covered, was unfavorable to the growth of 

 plants, otherwise, no doubt, lichens at least would have been seen. 

 Large ravens were circling about overhead, apparently quite unaffected 

 by the rarity of the atmosphere, as they seemed to fly with just as 

 much ease as at the level of the sea. 



" The great extent of the modern alluvial deposit concealed, in a 

 great measure the ancient rocks. At my encampment a ridge of very 

 hard limestone, dipping at a high angle, skirted the stream. Further 

 up the valley a hard slate occurred, and in another place a dark blue 

 slate, containing much iron pyrites, and crumbling rapidly when 

 exposed to the atmosphere. Fragments of this rock were scattered 

 over the plain in all states of decay. On the crest of the pass the 

 rock in situ was lime-stone, showing obscure traces of fossils, but too 

 indistinct to be determined ; the shingle, which was scattered over the 

 ridge, was chiefly a brittle black clay slate." 



Conceive a vast tract of country, the lowest valley of which is as 

 24* 



