346 J. B. Hatcher — Geology of Southern Patagonia. 



important water courses and many of the minor ones, which 

 now exist, were outlined. After this, there was a subsidence 

 sufficient to cause a submergence of this region beneath the 

 sea, which prevailed in Pliocene times for a period ample for 

 the deposition of the Cape Fairweather beds. Toward the 

 close of the Pliocene there began a gradual elevation of this 



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^^Oi '. ovi^.'^^^^^i ' i^^^; 1 ; 1 ;'; 1 ^ ' ? 



F 



Fig. 1. Section showing unconformity by erosion between Cape Fairweather 

 and Santa Cruz beds, made from top of laud slide just north of section shown in 

 %. 6. B. Upper 150 feet of S. C. beds; A. Marine 'C. F. beds, composed below 

 of sandstones with marine invertebrates and above of bowlder formation. 



area, during which the great bowlder formation was deposited 

 by the combined action of ice and water, and which resulted in 

 bringing this region permanently above sea level. There can 

 be little doubt that the origin of the numerous small salt lakes 

 which now occur all over this region, and which occupy depres- 

 sions in the surface of the plains, frequently several hundred 

 feet in depth, dates from this period, and that they are due to 

 confined bodies of salt water left in these depressions by the 

 receding sea. Such depressions were, at some period during 

 the elevation of this area, bays, formed usually near the source 

 of small drainage channels tributary to the more important 

 water courses, which existed in the former period of erosion. 

 Across the mouths of these shallow bays there were thrown, 

 by the tides, bars composed of sand and shingle which, as the 

 elevation continued, confined considerable bodies of sea-water. 

 If in such a body of water the loss by evaporation exceeded 

 the gain by tributaries, there would be a gradual decrease in the 



