WILLIS J GENERAL GEOLOGIC NOTES 27 



than the upper, but exhibits similar evidences of erosion and eolian 

 deposition. At Miramar and Necochea the formation, which is 

 exposed in the low bluffs also, consists of loess-like alluvium, the sur- 

 face of which has been eroded and filled in by wind. Similar char- 

 acters may be seen at Monte Hermoso and, as shown in plates 2 and 3, 

 at Mar del Plata. According to Ameghino, the exposure at Monte 

 Hermoso shows at the base a member of the Pampean terrane which 

 is even older than the lowest exposed in the Barrancas de los Lobos. 

 There is nothing in the lithologic or physical characters of the 

 deposit which would enable one to form an opinion on this point. 

 Ameghino's view is based on the faunas of the respective localities. 



Whatever the relative ages of the various deposits that are to be 

 seen in the sea cliffs of the eastern coast may be, they all exhibit the 

 evidence of identical physical conditions and point to alternations of 

 humidity and aridity during the time of their distribution. 



It is not necessary to pursue in detail the geologic and chrono- 

 logic problems connected with these older formations of the Pam- 

 pean, for the present investigation is concerned primarily only with 

 those formations which are related to the problem of man's existence 

 in the region, and the writers have not been able to find any evidence 

 which would show that he lived during Pampean time. Human 

 remains have been found, so far as the writers have been able to 

 observe, only in recent deposits, some of which are classed by them 

 as the Upper Pampean and others as post-Pampean formations. The 

 later phases of the Pampean may now be considered. 



Upper Pampean and Post-Pampean 



To Dr. Santiago Roth the writer is indebted for having pointed out 

 the distinction between the Upper Pampean and the Middle Pampean 

 of Roth's classification, as exposed in sections near La Plata; near 

 Anchorena, on the Rio de la Plata above Buenos Aires; in the Arroyo 

 de Ramallo; and at San Lorenzo, near Rosario. Doctor Ameghino 

 designated as Upper Pampean two deposits seen at and near Mar del 

 Plata. 



All of the deposits which were thus referred to the Upper Pam- 

 pean are characterized by the features which distinguish eolian loess. 

 The material is finely pulverent, not firmly consolidated, often colum- 

 nar in structure; it is light-gray or fawn colored and contains sec- 

 ondary limestone only in relatively small amount as compared with 

 the older Pampean formations. It is a formation which obviously 

 is composed of material eroded by the wind from the older Pampean 

 and redeposited in favorable localities in the form of eolian drifts. 

 It does not appear probable, considering the conditions of develop- 

 ment and the present irregular distribution, that the Upper Pampean 

 ever formed a widespread mantle in the region of its occurrence. It 



