362 BUEEAU OF AMERICAN ETHNOLOGY [bull. 52 



relation impossible. The Pampean terrane, which forms the base 

 of the section, contains a notable fauna and the geologic age of the 

 formation has been much discussed. General opinion places it 

 among the lowest or as the lowest of the divisions of the Pampean, 

 and Ameghino regards it as Miocene. The writer does not consider the 

 age of the so-called Monte Hermoso formation definitely establislied. 

 About half a kilometer southwest of the old lighthouse on Monte 

 Hermoso the writer observed the following section (see pis. 57, 58) : 



Dune sand, forming a steep grass-grown slope, part of the re~ 

 cent dune formation that constitutes a belt (3 kilometers or 

 more in width along this part of the coast) ; at the base is a 

 layer 15 to 40 cm. thick composed of gray sand, angular 

 pieces of gray sandstone and pebbles, some fractured by man; 

 marking an unconformity with the underlying formation. 

 Unconformity b}'' erosion. 



Gray sands, finely stratified, up to 1 meter exposed,. forming a 

 vertical face. 



Volcanic ash, in the form of hard white rock, forming a project- 

 ing ledge ; thiclaiess 20 to 40 cm. 



Gray sands, strongly cross stratified, slightly indurated, like 

 those above the volcanic ash; forming an undercut slope; 

 thickness 1^ meters. 



Gray sand, with small white quartz pebbles and very small 

 black pebbles, constituting a basal conglomerate at the bot- 

 tom of the gray sands. 

 Unconformity by erosion. 



Loess-loam, a yellow-brown compact earth, which is fine- 

 grained like loess but lacks the columnar structure of typical 

 eolian loess and is distinguished by firmness like soft pipe- 

 stone; lies upon a wind-eroded surface of the underlying for- 

 mation and has a pebbly structure, i. e. contains pebbles of 

 loess where it fills hollows. These wdnd-eroded hollows and 

 the filling by loess that contains wind-rolled pebbles of loess 

 mark an uncomformity by erosion like those observed in the 

 Barrancas del Norte, near Mar del Plata; 2^ to 3 meters. 

 Unconformity by erosion. 



Secondary limestone or tosca; locally developed in a thin 

 irregular plate. 



Loess-loam or loess-sandstone, a red-brown sandy earth, 

 very fine-grained, very compact and without lines of stratifi- 

 cation or vertical structure; 1 to 1^ meters. 



Beach. 



The features of this section are shown in plates 57 and 58 (from 

 photographs). It comprises three recognized formations, which 



m 

 O 



w 



H 

 'A 

 O 



