The Andes of southern Peru . d in verylow latitudes it is necessary to turn aside for a moment and con-sider two rival hypotheses of glacial retreat. First we have thehypothesis of periodic retreat, so generally applied to terminalmoraines and associated outwash in glaciated mountain implies also an advance of the ice from a higher position,the whole taking place as a result of a climatic change fromwarmer to colder and back again to warmer. But evidences of more extensive mountain glaciation in thepast do not in themselves prove a change in climate over the wholeearth. In an epoc
The Andes of southern Peru . d in verylow latitudes it is necessary to turn aside for a moment and con-sider two rival hypotheses of glacial retreat. First we have thehypothesis of periodic retreat, so generally applied to terminalmoraines and associated outwash in glaciated mountain implies also an advance of the ice from a higher position,the whole taking place as a result of a climatic change fromwarmer to colder and back again to warmer. But evidences of more extensive mountain glaciation in thepast do not in themselves prove a change in climate over the wholeearth. In an epoch of fixed climate a glacier system may so deeplyand thoroughly erode a mountain mass, that the former glaciersmay either diminish in size or disappear altogether. As the workof excavation proceeds, the catchment basins are sunk to, and atlast below, the snowline; broad tributary spurs whose snowsnourish the glaciers, may be reduced to narrow or skeleton ridgeswith little snow to contribute to the valleys on either hand; the. Fig. 137.
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Keywords: ., bookcentury1900, bookdecade1910, bookidandeso, booksubjectgeology
