286 PATAGONIAN EXPEDITIONS! GEOGRAPHY. 



seen, by the lofty escarpments of the sea, is covered with a thin veneer 

 of soil, which vainly endeavors to conceal the rocks beneath and is scantily 

 covered with grass. Occasionally bushes, seldom attaining a height of 

 more than five or six feet, appear in specially favored localities. Bands of 

 guanacos, 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 traveller, 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 diam- 

 eter and from 100 to nearly 1,000 feet in depth, as observed 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 reduced by evaporation, and beds of almost 

 pure salt are precipitated, occasionally attaining a thickness of several feet. 



An examination of the depressions 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 situ- 

 ated. All this leads to the inference that these are residual lakes, left as 

 confined bodies of water at the final elevation of the land above sea-level 

 and, further, that the depressions are remnants of former drainage sys- 

 tems, existing prior to the last submergence, and corresponding approxi- 

 mately, though not entirely, to those of to-day. 



Other notable features are the broad, deep, transverse valleys that 

 cross Patagonia from west to east and form the chief drainage sys- 

 tems. These are all true valleys of erosion, and along their bottoms, in 

 most cases, still flow the streams by which they have been eroded ; though 

 in some instances, like the Desire and Coy Rivers, there are now only 

 intermittent streams, while in the valley of San Julian no stream at present 

 ever flows, the waters of the original stream having been captured long 

 since, at a distance of about 100 miles from the coast, by a northern tribu- 

 tary of the Santa Cruz. The latter, in the volume of its waters, is much 

 the most important river of the southern Patagonian plains. 



Another important feature characteristic of these plains is the series of 

 escarpments, often several hundred feet in height, that terminate a succes- 

 sion of terraces encountered at varying elevations, as one proceeds from the 



