OVER THE ARKA-TAGH 
1007 
mountain -range I had before noticed in the south. It 
was, we afterwards discovered, a continuation of the Koko 
shili Mountains. Between the two ranges extended the 
broad tableland already mentioned, its eastern horizon 
forming a perfectly straight line, scarcely perceptible at 
its southern extremity. Towards the west too both ranges 
stretched as far as the eye could see, but the country 
between them was more diversified. 
The little hill on which I stood was very interesting. 
The bare rock, the usual dark green slates, cropped out 
on its north-eastern and eastern flanks at an angle of 
16° to the north-north-west. But its summit was apparently 
capped by a horizontal layer of blue-black tuff, some 
sixteen feet thick, with numerous round and elliptical 
vesicles, partly flllecl with a white mineral .substance. The 
tuff itself was a good deal weathered, and numerous sharp 
angular pieces lay scattered about on its surface. I also 
observed several other isolated hills similarly capped with 
tuff farther to the south. 
As I walked back to my tent, Yolldash at my heels, the 
sun was already setting in a sky as pure and blue as 
turquoise, save that a few snow-white fleecy clouds (cirri- 
cumuli) floated along In isolated groups. But hardly 
had the upper edge of the sun disappeared below the 
horizon, when its place in the west was taken by a black, 
threatening mass of cloud. Close down upon the earth 
the atmosphere was perfectly calm, but in the higher 
regions it was blowing hard, as we saw from the dark 
steel-grey clouds, whose edges were tinted various shades 
of blood red, vivid yellow, and violet by the setting .sun. 
Some portions of the clouds were entirely black ; others 
reluctantly allowed the .sheaf of the sun’s rays to penetrate 
through them. It was a sublime, and yet a fantastic, 
an awe-inspiring spectacle. I could not tear my eyes 
away from it. Then came the first puffs of wind, ruffling 
the calmness of the atmosphere, at first feeble and in 
Intermittent gusts, but soon more violently as well as 
more frequently. The squall swooped down upon the 
camp. The wind blew with indescribable fury. The men 
