20 BUEEAU OF AMERICAN ETHNOLOGY [bull. 52 



ever since the uplift of the mountains occasioned the erosion which 

 produced the Pampean sediment, and it is reasonable to infer that 

 the fineness of the deposit is due to eolian sorting in the desert regions 

 through which the rivers flow. This inference probably could not be 

 extended to sediments derived from central Brazil, but it may be 

 stated that the Pampean terrane which is so derived is less charac- 

 teristically eolian than that which occurs farther west and south. 



The parallel with the Hwang River may be extended to the action 

 of the wind in the delta plain. During the winter months, in North 

 China, when there is no rain or snow and no protecting vegetation 

 dust is constantly in the air and dust storms are serious. Eolian 

 drifts accumulate in eddies and lees. Similar conditions have existed 

 during the formation of the Pampean, for it comprises both relatively 

 modern and older deposits of a strictly eolian character occurring 

 with others laid down by the river waters or in ponds. 



It is possible that the geographic and seasonable conditions which 

 have been described may be found sufficient to explain the various 

 aspects of the Pampean terrane. But it is possible also that climatic 

 cycles have been an important factor in determining the variation and 

 succession of deposits in South America as they have been in the 

 northern hemisphere. In order to present this question in the light 

 of some of the known facts, we may digress at this point from the 

 description of the Pampean terrane to a discussion of the climatic 

 changes which characterize the Quaternary period in the Northern 

 Hemisphere. 



Here this period is distinguished from the Tertiary epochs w^hich 

 preceded it by the rigor of climate which occasioned the glaciation of 

 northern Europe and northeastern North America. Ice fields of 

 great extent spread from centers so conditioned by excessive snowfall 

 and comparatively low temperature that they served as gathering 

 grounds for the great neve which supplied the ice. 



These centers were determined by meteorologic and also by topo- 

 graphic conditions. In North America two of them were situated in 

 the great plains of northern Canada; another was in the northern 

 Cordillera. In Europe the principal fields whence proceeded the dis- 

 persion of the ice were in northern Germany and in the Alps. 



We were wont to speak of the Quaternary and of the glaciation 

 which characterized it as though it were a single glacial period with- 

 out intervals of milder climate. But this concept, which marked an 

 early stage in the investigation of glacial deposits, has long since 

 given way to the recognition of at least four epochs of glaciation and 

 three epochs of general interglacial climate in those regions where the 

 phenomena are most fully developed. 



The several epochs of the Quaternary have received names which 

 differ somewhat according to the center from which the ice spread. 



