hijdliCka] stone INDUSTRIES OF THE ARGENTINE COAST 113 



and deeper and often more irregular in form. In many instances 

 these larger depressions connect at one extremity with the seashore, 

 and their bottom in parts, or even in a large stretch reach to, or 

 even somewhat into, the ground beneath the sand. The basal areas 

 in the various depressions here referred to are sometimes called playas, 

 a convenient term for the purpose, though more strictly applied to the 

 beach only. 



There are two distinct varieties of the dune-range playas, which 

 may be distinguished by the color as the black and the gray. Most 

 of the black are shallower than the gray, though the difference may 

 be slight. They present level patches of closely packed fuie sand 

 and earth colored nearly black by manganese and possibly other 

 mineral ingredients; the surface is often rich in archeologic specimens. 

 These black playas are generally situated more inland, and owe their 

 principal characteristics of form and color to water action. They 

 represent the denser ground of the lowest parts of the dunes, or 

 the top of the underlying soil, with additional material brought and 

 deposited during rains. In heavier rains water in small quantities 

 evidently accumulates over the surface of these patches, particularly 

 of those that offer no easy outlet, and the mineral particles, as well 

 as fine sand from the surrounding dunes, settle and form the black 

 even surface. The amount of material tlius deposited is generally 

 small; yet it was found sufficient nearly to bury, in one instance, the 

 skull of a viscacha, and in other cases to cover, in a degree, several 

 stone flakes and implements. Generally, however, the stone objects 

 and bones lie free upon the surface. 



The second class of playas consists of the larger, sometimes exten- 

 sive, irregular, denuded surfaces, similar to eroded areas occurring 

 independently of sand dunes, as mentioned in the first part of this 

 section, and containing debris of tosca, stones, shells, bones, etc., and 

 also, in some localities, numerous pieces of scoria. In some places 

 such large denuded patches show remnants, a few inches to more 

 than 2 feet in height, of a former, comparatively recent surface, the 

 rest of which has been removed by the action of the elements. In 

 some instances the higher of such remnants are capped with darker 

 earth, which represents, in all probability, the vegetal layer that has 

 become covered by the sands. The gray floor itself belongs to older 

 sediments and shows traces, in some localities rare, in others rather 

 common, of skeletal remains of fossil animals, particularly the glypto- 

 don and the scelidotherium. Most of these gray open playas are 

 poor in specimens pertaining to man, although there may be sheltered 

 nooks farther inland in which more of such objects will be brought to 

 light in the future. 



21535°— Bull. 52—12 8 



