CLIMATE AND TERRESTRIAL DEPOSITS 175 



upon the piedmont slopes. The same is found to be true on the 

 eastern slopes of the southern Andes on portions of which aggradation 

 is now in active progress. An increased snowfall without actual 

 glaciation, especially if it takes the place of what had previously 

 fallen as rain, may therefore result in the waste being carried farther 

 before deposition, accompanied by a dissection of the upper portion 

 of the piedmont slope, the results being opposite to those of increased 

 frost action. In regions of less elevation, however, the rainfall and 

 snowfall are nearly the same upon upland and lowland, the volumes 

 of the streams are increased as they flow toward the sea, the sediment 

 once picked up is carried through by the river, and as a result of 

 increased snowfall an increased erosion may take place without the 

 tendency to aggradation in the middle portions of the streams. Such 

 an effect is in many ways equivalent to a change toward a more volumi- 

 nous or at least more concentrated regional rainfall. In the preceding 

 statements snow and frost action have been considered separately. 

 In nature, however, there may be various combinations of these 

 agencies. Increased cold may lessen the hold of the vegetation on 

 the soil, the latter, saturated in the spring with snow water, may be 

 more rapidly removed, and an opportunity be given for increased 

 frost action. Consequently, while a greater amount of sediment 

 may be carried through to the lower portions of the river system, 

 aggradation may yet take place to some extent in the upper portions. 

 Some such change of relations seems to have occurred during glacial 

 times over certain regions outside of the limits of glaciation, since 

 terraces and fans of glacial age characterize the upper portions of 

 many river systems. These conditions find their maximum develop- 

 ment at the present time in the subglacial polar or mountain climates. 

 The subject has been discussed by J. G. Andersson,' who shows 

 that the regolith, becoming saturated with snow water, creeps slowly 

 but bodily down even the gentler slopes. The production of new 

 waste is chiefly dependent upon frost action; so that the two results 

 of a lowering of temperature co-operate and it is not practicable cbarly 

 to separate them. The Gila conglomerate, however, on account of 

 the short distance which the bulk of the material was transported, 



I "Solifluction, a Component of Subaerial Denudation," Journal 0} Geology, 

 Vol. XIV, 1906, pp. 91-112. 



