RIVERS OF SOUTHERN PATAGONIA. 43 



down upon and across the valley of Coy River, or Rio Coyle, as it is 

 locally known. 



The valley of this stream has a breadth of from two to six miles 

 and supports a vegetation consisting for the most part of grasses, 

 which, as compared with those of the pampas, might be considered 

 almost luxuriant. 



The stream is small, seldom more than two rods in width, and usually 

 sluggish in its lower course. There are long stretches of still and quiet 

 waters alternating with occasional short rapids, as the confined waters 

 dash for a few rods over coarse beds of shingle. We reached Governor 

 Mayer's estancia, located some twenty miles above, early the following 

 morning. Wherever we approached the river, it was noticeable that the 

 surface of the water was but little beneath that of the valley, although this 

 was the season of low water. From this it has resulted that the soil for 

 a considerable distance on either side is subirrigated. This explains the 

 presence of beautiful stretches of bright green meadow lands clothed with 

 a luxuriant growth of tall waving grass. I later discovered that this was 

 true of all the less important rivers of southern Patagonia, such as the 

 Rio Sheuen, or Chalia, Rio Aubone, and the Rio Chico of the Gallegos, 

 while the larger rivers like the Gallegos, Santa Cruz, and the Rio Chico 

 of the Santa Cruz, are rapid streams with deeper channels cut in valleys 

 that are as a rule quite as arid and destitute of vegetation as are the sur- 

 rounding plains. This difference is evidently due to the fact that the 

 larger streams have their sources far back in the Andes, where they are 

 fed by numerous glaciers or mountain streams coming from the region of 

 perpetual snow and hence have a constant and never-failing water supply, 

 continuous throughout the year, with an erosive power sufficient at all 

 times to keep their channels open. With the smaller streams it is quite 

 different. They head on the plains or in the low foothills at the eastern 

 base of the Andes. Their water supply is, therefore, precarious and inter- 

 mittent, and, during the long dry season, falls so low that for long distances 

 throughout their lower courses their channels are dried up and destitute 

 of water, so that the materials brought down by the upper courses of such 

 streams, instead of being carried out to sea, are thrown down just above 

 where the flow of water ceases, resulting in the gradual silting up of the 

 channel and the formation of the series of rapids or riffles and stretches 

 of still water just referred to, through the inability of the stream to keep 



