GEOGRAPHIC FEATURES OF SOUTHERN PATAGONIA 43 



beds. They are of marine origin and contain, in great abundance, 

 the remains of marine invertebrates. I should also add that through- 

 out the entire extent of tliis coast the uppermost crest of the bluffs 

 is composed of from 20 to 30 feet of unstratified boulders and claj's, 

 constituting the great Shingle formation of Patagonia, distributed 

 somewhat uniformly over almost the entire surface, and of probably 

 combined ice and aqueous origin. 



M'ith this hast}' survey of the eastern coast line, let us proceed into 

 the interior. Ascending the bluff we emerge upon a broad, elevated 

 plain, stretching westward to the base of the Andes and abruptl}^ 

 terminated on the east, as we have seen, b}'' the lofty escarj)ments of 

 the sea. Its surface, with a thin veneer of soil vainly endeavoring to 

 conceal the rocks beneath, is scantily covered with grass. Occasional 

 bushes, seldom attaining a height of more than five or six feet, appear 

 in specially favored localities. Bands of guanaco, or South American 

 camels, and flocks of rheas, the so-called ostrich, feed here in great 

 numbers and provide the chief sustenance of the Patagonian traveler, 

 as also of the Patagonian Indian. 



Scattered over the surface of the plains in considerable numbers 

 are great depressions, or rather excavations, frequently several miles 

 in diameter and from 100 to more than 1,000 feet in depth, as ob- 

 served in some instances near the base of the Andes. The bottoms 

 of these depressions are usually occupied by small saline lakes. In 

 periods of drought, which occur annually in this region, usually from 

 December to April, the volume of water in such lakes is much re- 

 duced by evaporation, and beds of almost pure salt are precipitated, 

 occasionall}^ attaining a thickness of several feet. 



An examination of the de[)ressions occupied by such lakes reveals 

 the fact that the bluffs on one side are always much lower than those 

 on the other sides, and, further, that the lower side always lies toward 

 the present drainage system of the particular region in which the 

 lake is situated. All, this leads to the inference that these are resid- 

 uary lakes, left as confined bodies of water at the final elevation of 

 the land above sea-level, and, further, that the depressions are rem- 

 nants of former drainage systems, existing i)rior to the hist submer- 

 gence, and corres[»onding api)roximately, thougli not entirely, wiili 

 those of today. 



Other features to be noticed are tlie brcxid, deep, transverse valleys 

 that cross Patagonia from west to east and form the (;hief drainage 

 systems. These are all true valleys of erosion, and along their l)ot- 



