168 THE PLAIN OF THE PAMPAS 



an intense eruptive activity during or before their 

 formation.^ Doering had already noticed in the 

 Cordoba region the prevalence of beds of volcanic ash, 

 which become thicker as one approaches the sierra. 

 It is certain that the Pampean sierras have had their 

 share in the formation of the Pampean beds. But 

 the main mass is probably of Andean origin. However 

 that may be, as soon as one gets away from the fringe 

 of the mountains, the only variety noticeable in the 

 lands of the Pampa is that which they owe to the 

 conditions in which they have been deposited. 



River deposits strictly so called, estuary deposits, 

 lagoon deposits, asolian deposits, aeolian deposits redis- 

 tributed by water, river deposits redistributed by 

 wind — all these different types are represented in the 

 Pampean formation, but their relative importance is 

 still disputed.' 



• In Ales Hrdlicka, Early Man in South America (Smithsonian 

 Instit. Bull., 52, Washington, 1912). 



^ Many attempts have been made to classify the Pampean lands, 

 but the results cannot be regarded as linal. Ameghino, who is first 

 and foremost a palaeontologist, has done a service in showing the 

 futility of these geological divisions based upon the actual surface 

 of the deposits (colour, fineness, etc.). But even paljeontology gives 

 rather uncertain results, as it is impossible to recognize and follow 

 step by step the various stages of the movement of the fossils. All 

 the classifications of the Pampean are based upon a study of two 

 groups of sections. The first group comprises the cliff on the right 

 bank of the Parana from Rosario to Buenos Aires and the coastal 

 cliff which is a continuation of it, with a break from Ensefiada at 

 Mar Chiquita to Bahia Bianca. Ameghino has recognized there a 

 thick series of aeolian deposits separated by several discordances, the 

 oldest elements of which, at Bahia Bianca, belong to the Miocene. 

 The second group comprises the cliffs which enclose the valley of 

 the Rio Primero above and below Cordoba. Doering and Bodenbender 

 in this case describe two stages of aeolian loess, each covered by torrential 

 gravel. 



From the study of these sections geologists have drawn certain 

 conclusions as to the movements which have affected the soil of the 

 Pampa and the changes which the climate has experienced. These 

 conclusions have in each case only a local value, and they have not 

 yet been co-ordinated. The majority of the observers, from Doering 

 to Bailey Wilhs and RoveretO; seem not to have taken into account 

 sufl&ciently the fact that in the continental formations the most diverse 



