maximum precipitation on the mountain slopes in the glacial period are illustrated in the diagram, Figure 115. Penck has made similar studies at the southern end of the Puna, where he finds a zone of maximum precipitation whose upper limit at the present time is 4000 meters and whose lower limit is about 3000 meters. Within the upper limit is snowfall in the winter season and occasionally at other times of the year. From the evidence of the carved valley walls and flat floors
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Fig. 115—A represents the upper and lower limits of the zone of maximum precipitation at the present time; B, the limits of Pleistocene time. I, II, and III are mountains of different height and relationship to these two positions of the rainfall belt.
Penck concludes that the present snow line is 600 or 800 meters, that is to say 2000 or 3000 feet, above the snow line of the glacial period.[1] There is snow at 5300 meters on Aconquija; on Tres Cruces in the same latitude (27° S.) in the Western Cordillera the lower limit of permanent snow is at 6300 meters, or a range of 17,000 to 21,000 feet. In southern Peru I found the snow line between 16,000 and 18,000 feet with local varia- tions dependent upon topographic conditions. Where the glaciers of the present time do not descend below 14,000 feet, I found them to have descended to 11,000 feet in the Ice Age. I concluded that the snow line of the glacial period was 1000 meters, or over 3000 feet, lower than now.”
The effect of this great change in climate in the glacial period must have been clearly felt upon the well-defined zones of pasture and of woodland or forest on the border of the mountains. This is particularly true in northwestern Argentina, where the belt of woodland is so narrow and patchy that any increase of rainfall through the lowering or raising
- ↑ Penck, op. cit., pp, 251 et al.
