THE COUNTRY OF THE SHEPHERDS 53 



pastures, or were they driven to them? Do they live here by 

 choice or of necessity? The answer to these questions introduces 

 two other geographic factors of prime importance, the one phys- 

 ical, the other economic. 



The main tracts of lofty pasture above Antabamba cover moun- 

 tain slopes and valley floor alike, but the moist valley floors supply 

 the best grazing. Moreover, the main valleys have been inten- 

 sively glaciated. Hence, though their sides are steep walls, their 

 floors are broad and flat. Marshy tracts, periodically flooded, are 

 scattered throughout, and here and there are overdeepened por- 

 tions where lakes have gathered. There is a thick carpet of grass, 

 also numerous huts and corrals, and many flocks. At the upper 

 edge of the main zone of pasture the grasses become thin and with 

 increasing altitude give out altogether except along the moist val- 

 ley floors or on shoulders where there is seepage. 



If the streams head in dry mountain slopes without snow the 

 grassy bands of the valley floor terminate at moderate elevations. 

 If the streams have their sources in snowfields or glaciers there is 

 a more uniform run-off, and a ribbon of pasture may extend to the 

 snowline. To the latter class belong the pastures that support 

 these remote people. 



In the case of the Maritime Andes the great elevation of the 

 snowline is also a factor. If, in Figure 25, we think of the snow- 

 line as at the upper level of the main zone of pasture then we 

 should have the conditions shown in Figure 36, where the limit of 

 general, not local, occupation is the snowline, as in the Cordillera 

 Vilcapampa and between Chuquibambilla and Antabamba. 



A third factor is the character of the soil. Large amounts of 

 volcanic ash and lapilli were thrown out in the late stages of vol- 

 canic eruption in which the present cones of the Maritime Andes 

 were formed. The coarse texture of these deposits allows the 

 ready escape of rainwater. The combination of extreme aridity 

 and great elevation results in a double restraint upon vegetation. 

 Outside of the moist valley floors, with their film of ground 

 moraine on whose surface plants find a more congenial soil, there 

 is an extremely small amount of pasture. Here are the natural 



