CLIMATOLOGY OF THE PERUVIAN ANDES 155 



low. The break between the two, a topographic unconformity, 

 may be distinctly traced. 



Combined with these topographic features are certain climatic 

 features of equal precision. Between 7,000 and 13,000 feet is a 

 zone of clouds oftentimes marked out as distinctly as the belt of 

 fog on the Peruvian coast. 6 Earely does it extend across the val- 

 ley. Generally it hangs as a white belt on the opposite walls. 

 When the up-valley winds of day begin to blow it drifts up-valley, 

 oftentimes to be dissolved as it strikes the warmer slopes of the 

 upper valley, just as its settling under surface is constantly being 

 dissolved in the warm dry air of the valley floor. Where the pre- 

 cipitation is heaviest there is a belt of woodland — dark, twisted 

 trees, moss-draped, wet — a Druid forest. Below and above the 

 woodland are grassy slopes. At Incahuasi a spur runs out and 

 down until at last it terminates between two deep canyons. No 

 ordinary wells could be successful. The ground water must be 

 a thousand feet down, so a canal, a tiny thing only a few inches 

 wide and deep, has been cut away up to a woodland stream. 

 Thence the water is carried down by a contour-like course out of 

 the woodland into the pasture, and so down to the narrow part of 

 the spur where there is pasture but no springs or streams. 



Corn fields surround the few scattered habitations that have 

 been built just above the break or shoulder on the valley wall 

 where the woodland terminates, and there are fine grazing lands. 

 The trails follow the upper slopes whose gentler contours permit 

 a certain liberty of movement. Then the way plunges downward 

 over a staircase trail, over steep boulder-strewn slopes to the arid 

 floor of a tributary where nature has built a graded route. And 

 so to the still more arid floor of the main valley, where the ample 

 and moderate slopes of the alluvial fans with their mountain 

 streams permit plantation agriculture again to come in. 



To these three climates, the western border type, the eastern 



8 Speaking of C6mas situated at the headwaters of a source of the Perene amidst 

 a multitude of quebradas Raimondi (op. cit., p. 109) says it "might properly be called 

 the town of the clouds, for there is not a day during the year, at any rate towards 

 the evening, when the town is not enveloped in a mist sufficient to hide everything 

 from view." 



