CLIMATOLOGY OF THE PERUVIAN ANDES 139 



larger than a wash basin. It lay in a valley that headed in the 

 Coast Kange, and carried down into the desert a mere trickle that 

 seeped through the gravels of the valley floor. A little below the 

 pool the valley cuts through a mass of granite and becomes a steep- 

 walled gorge. The bottom is clogged with waste, here boulders, 

 there masses of both coarse and fine alluvium. The water in the 

 valley was quite incapable of accomplishing any work except that 

 associated with solution and seepage, and we saw it in the wet 

 season of an unusually wet year. Clearly there has been a diminu- 

 tion in the water supply. But time prevented us from explor- 

 ing this particular valley to its head, to see if the reduction 

 were due to a change of climate, or only to capture of the 

 head-waters by the vigorous rain-fed streams that enjoy a favora- 

 ble position on the wet seaward slopes and that are extending 

 their watershed aggressively toward the east at the expense of 

 their feeble competitors in the dry belt. 



An early morning start enabled me to witness the whole series 

 of changes between the clear night and the murky day, and to pass 

 in twelve hours from the dry desert belt through the wet belt, and 

 emerge again into the sunlit terraces at the western foot of the 

 Coast Eange. Two hours before daylight a fog descended from 

 the hills and the going seemed to be curiously heavy for the beasts. 

 At daybreak my astonishment was great to find that it was due 

 to the distinctly moist sand. We were still in the desert. There 

 was not a sign of a bush or a blade of grass. Still, the surface 

 layer, from a half inch to an inch thick, was really wet. The fog 

 that overhung the trail lifted just before sunrise, and at the first 

 touch of the sun melted away as swiftly as it had come. With it 

 went the surface moisture and an hour after sunrise the dust was 

 once more rising in clouds around us. 



We had no more than broken camp that morning when a 

 merchant with a pack-train passed us, and shouted above the 

 bells of the leading animals that we ought to hurry or we should 

 get caught in the rain at the pass. My guide, who, like many of 

 his kind, had never before been over the route he pretended to 

 know, asked him in heaven's name what drink in distant Camana 



