22 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



there is evidence in the Pampean, is from humid to arid and back to 

 humid, probably a number of times. It is theoretically probable that 

 the epochs of humid climate were the more genial and those of arid 

 climate the more rigorous as regards temperature, but of that we have 

 as yet no satisfactory evidence. 



With these suggestions we may consider some ot the evidences of 

 climatic variation in the Pampean. 



Sections of the Pampean are to be seen at various points along the 

 eastern coast of Argentina and have been observed by the writer 

 north of Mar del Plata, in the Barrancas de los Lobos south of that 

 city, and along the coast farther southeastward at Miramar, Necochea, 

 and Monte Hermoso. The sections were carefully studied in each 

 locality, but since we require here only an illustration of the kind 

 of evidence of climatic change that may be adduced, it will suffice 

 to describe a characteristic relation observed in the Barrancas del 

 Norte, north of Mar del Plata. 



The Barrancas del Norte are sea cliffs which vary but little from 

 an average height of 10 meters. The constituent materials are 

 earths which differ in color, texture, and arrangement, and which 

 inclose secondary deposits of carbonate of lime forming more or less 

 irregular bodies. The earths are characteristic loams of the Pam- 

 pean terrane. They are very fine and uniform and usually very free 

 from sands; pebbles, except those of the secondary limestone, are 

 entirely wanting. In color, they present shades of brown which 

 may be described as dark or reddish or fawn-colored. Gray tones 

 also occur and certain strata are distinctly greenish. They are often 

 compared to the Chinese deposits, to which Richthofen gave the 

 name loess, and they share with the material the quality of uniform 

 fineness. They are more compact, however, and exhibit many 

 details of constitution and structure not found in loess, while at the 

 same time they usually lack the columnar structure nearly always 

 characterizing loess. 



In the Barrancas del Norte the constituent formations might be 

 variously classified as forming two, three, or four distinct horizons. 

 From summit to base of the cliff one may recognize — 



Plain : Meters. 



Black soil derived from the Pampean by the introduction of humus and 



possibly by accumulation of dust in the grass 1 



Fawn-colored to gray, or reddish, or yellow-brown Pampean earths, very 



irregularly distributed and varied in structure 4-8 



Greenish, stratified, sometimes sandy, but in general earthy, deposits not 



always present 0-2 



Dark brown, very compact, dense earths, often sandy and constituting an 



earthy sandstone 0-3 



Beach 10 



