Note 82 — Chapter VI · THE PLAIN OF THE PAMPAS

Many attempts have been made to classify the Pampean lands, but the results cannot be regarded as final. Ameghino, who is first and foremost a palæontologist, 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 palæontology 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 Paraná from Rosario to Buenos Aires and the coastal cliff which is a continuation of it, with a break from Enseñada at Mar Chiquita to Bahía Blanca. Ameghino has recognized there a thick series of æolian deposits separated by several discordances, the oldest elements of which, at Bahía Blanca, belong to the Miocene. The second group comprises the cliffs which enclose the valley of the Rio Primero above and below Córdoba. Doering and Bodenbender in this case describe two stages of æolian 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 Willis and Rovereto, seem not to have taken into account sufficiently the fact that in the continental formations the most diverse deposits may come next to each other in the same series, according to the particular process of deposition, and that their alternation does not imply a general change in the conditions of erosion.