56 THE ANDES OF SOUTHERN PERU 



society corresponding to the superimposed strata of climate and 

 land. 



At Salamanca (Fig. 62) I saw this admirably displayed under 

 circumstances of unusual interest. The floor and slopes of the 

 valley are more completely terraced than in any other valley I 

 know of. In the photograph, Fig. 30, which shows at least 2,500 

 feet of descent near the town, one cannot find a single patch of sur- 

 face that is not under cultivation. The valley is simply filled with 

 people to the limit of its capacity. Practically all are Indians, but 

 with many grades of wealth and importance. When we rode out 

 of the valley before daybreak, one September morning in 1911, 

 there was a dead calm, and each step upward carried us into a 

 colder stratum of air. At sunrise we had reached a point about 

 2,000 feet above the town, or 14,500 feet (4,420 m.) above sea level. 

 We stood on the frost line. On the opposite wall of the valley the 

 line was as clearly marked out as if it had been an irrigating canal. 

 The light was so fully reflected from the millions of frost crystals 

 above it that both the mountainside and the valley slopes were 

 sparkling like a ruffled lake at sunrise. Below the frost line the 

 slopes were dark or covered with yellow barley and wheat stubble 

 or green alfalfa. 



It happened that the frost line was near the line of division 

 between corn and potato cultivation and also near the line separat- 

 ing the steep rough upper lands from the cultivable lower lands. 

 Not a habitation was in sight above us, except a few scattered 

 miserable huts near broken terraces, gullied by wet-weather 

 streams and grown up to weeds and brush. Below us were well- 

 cultivated fields, and the stock was kept in bounds by stone fences 

 and corrals ; above, the half -wild burros and mules roamed about 

 everywhere, and only the sheep and llamas were in rude enclo- 

 sures. Thus in a half hour we passed the frontier between the 

 agricultural folk below the frost line and the shepherd folk above 

 it. 



In a few spots the line followed an irregular course, as where 

 flatter lands were developed at unusual elevations or where air 

 drainage altered the normal temperature. And at one place the 



