HRDLi^KA] SKELETAL EEMAINS OF EAKLY MAN 363 



Ameghino has named Monte Hermosean, Puelchean, and Recent, and 

 which are separated by distinct unconformities. 



The Monte Hermosean formation comprises the two deposits of 

 brown earth or loess-loam, which are themselves separated by a plane 

 of wind erosion. The formation is regarded as Miocene by Ameghino 

 and as older than any other exposure of the Pampean. 



The Puelchean consists of the stratified, slightly indurated, gray 

 sands or sandstone, both above and below the volcanic ash, between 

 two unconformities by erosion. It is a peculiar sandstone, marked 

 by very striking cross stratification and uniformity of gray color and 

 grain. The writer regards it as an eolian formation. Later in the 

 season, when studying the section exposed along the Rio Colorado 

 from the delta to Pichi-Mahuida, he observed a very similar sand- 

 stone, which might be correlated with the Puelchean on grounds 

 of lithologic identit}^. It is a thick widespread formation which is 

 regarded as a Tertiary sandstone. The Pulechean, if the same, 

 represents only a thin edge of it. 



The Recent formation, as exposed in this section, is but a part 

 of the extensive deposit of dune sands, which has become grass-grown 

 and so fixed, but which does not yet show any signs of erosion. In 

 driving some 10 kilometers diagonally across the belt the writer 

 noted a general similarity to the grass-grown dunes observed north 

 of Necochea, but near Monte Hermoso the supply of sand appears to 

 have been much greater. The belt is very wide and the sand hills are 

 high. 



The distinction between the Recent dune sands and the Tertiary ( ?) 

 Puelchean is not obvious. The two are identical in constitution; 

 they are both eolian and may exhibit similar structures; the Recent 

 formation ma}^ be consolidated almost or quite to the firmness of the 

 older one. The unconformity between them suffices to establish 

 the difference in age and is unmistakable when clearly shown in 

 section (pis. 57, 58). Arrowheads or hand-chipped stones associ- 

 ated with the sands would mark them as recent, such objects being 

 common in the belt of sand dunes which the Indians were in the habit 

 of using as a line of march and cover in attacking Argentine settle- 

 ments. At Monte Hermoso the dune sands and associated chipped 

 stones had fallen from the upper slope onto various projecting ledges 

 and chips were collected from the surfaces of the Monte Hermoso 

 terrane. 



Through the courtesy of Doctor Ameghino the writer saw at 

 Buenos Aires 10 pieces of burnt clay which would appear to have 

 formed a layer about 10 by 15 cm. in area and 5 to 10 mm. thick, 

 collected by Ameghino from the Monte Hermosean formation below 

 high-tide level. As stated in describing certain observations on 

 the burnt earth of the Pampean, the writer finds that clays of that 



