32 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



elevated, may retain its integrity. The drainage systems have not 

 had time to develop since the Pampean was warped up to its present 

 position. 



Thus observations of the effects of erosion along the Parana and in 

 the valley of the Salado show that streams have done very little work 

 on the Pampean formation. Indeed, the features which they have 

 sculptured are insignificant. Hence, the elevation of the pampas may 

 be regarded as recent. If, however, it should appear on further study 

 that stream erosion has been retarded by the peculiar character of 

 the pampas to a greater degree than now seems probable, and that 

 there have been one or more epochs of aridity during which stream 

 erosion was reduced to practically nothing, there would be reason for 

 extending the time that has elapsed since the uplifting of the surface, 

 and it might be that this later history would cover the Quaternary- 

 period. 



It has already been stated that those eolian deposits, which are 

 characterized as Upper Pampean by both Roth and Ameghino, he in 

 hollows sculptured in the surface of the Pampean, and the same holds 

 true for the still younger deposits of alluvium and dune sands. All of 

 these, including the Upper Pampean, appear to the writer to fall in 

 the Quaternary. It may or may not follow that the earlier Pampean 

 formations were deposited during the later Tertiary (Pliocene and 

 late Miocene), though this is probable; but they also may be in part 

 of the Quaternary age. 



ATLANTIC COAST OF THE PAMPAS 



If now we turn from the consideration of the pampas to that of the 

 eastern coast of Argentina, we must recognize at once that the coast 

 line has reached its present position by virtue of wave erosion on the 

 uplifted mass of the Pampean. In order to place this proposition in 

 its appropriate relations, we may consider the development of the 

 coast as the result of the attack of the ocean on the inert mass of the 

 Pampean earths. 



A shore is fashioned by waves and currents, driven chiefly by winds. 

 In the course of their attack they destroy headlands, build bars, 

 spits, and beaches across embayments, and eventually establish a 

 coast which is adjusted to and in equilibrium with their activities. 

 A young coast is distinguished by irregularity, an old coast by 

 smoothness. On a young coast the wave-cut terraces and sea chffs 

 are conspicuous features; on an old coast the chffs due to wave action 

 are modified or obUterated by subaerial erosion. It may happen 

 that sea cliffs cut in enduring rock stand for a relatively long time, 

 but a chff of earth, however compact, is a very transient feature. 



