240 PATAGONIAN EXPEDITIONS: GEOGRAPHY. 



proportions. It is here a stream with an average width of perhaps two 

 hundred feet, a depth of about three feet and a current averaging perhaps 

 four miles an hour. Its waters flow constantly throughout its whole course 

 and during the entire year. It has its source in a number of smaller 

 streams which rise in the higher pampas and lower Andes between 

 parallels 51° 30' and 53° of south latitude. The area drained by it is, 

 therefore, not very extensive. Its valley, though more considerable than 

 that of the Chico, cannot be considered as one of the deeper transverse 

 valleys of this region. Though extending well within the foothills of 

 the Andes, none of its more important tributaries reach the limits of per- 

 petual snow, so that for a considerable portion of each year it is dependent 

 upon the precipitation for its water supply. At such seasons it is very 

 sensibly affected by periodical floods and drouth. 



The Coy River and its Tributaries. — This river discharges its waters 

 into Coy Inlet in south latitude 51°. It drains practically all the country 

 east of the Andes and between the Santa Cruz and Gallegos Rivers. 

 Although its drainage area considerably exceeds that of the Gallegos, it 

 has a smaller volume of water. It falls among the rivers which have been 

 classed as intermittent, and, owing to the greater elevation which has taken 

 place in this region, its valley is considerably deeper than that of either 

 of the two previously considered streams. All of its tributaries have their 

 sources on the high plains just east of the base of the Andes, and none 

 may be said to extend into the mountains. The conditions that prevail 

 throughout the course of this stream are in every way similar to those 

 that have been described as existing in the course of the Rio Chico of the 

 Gallegos, except that the desiccated portion of the Coy River extends 

 much farther from the coast, reaching even to the forks of that stream, 

 although there are some considerable marshes below this point. To the 

 northward of the Coy River a high pampa extends, gradually increasing 

 in altitude, through the combined effects of a succession of terraces and 

 the gradual southeasterly slope of the general surface, until the very crest 

 of the high bluff overlooking the deep valley of the Santa Cruz River is 

 reached. Owing to this somewhat remarkable and peculiar topographic 

 feature, the entire country immediately south of the valley of the Santa 

 Cruz is drained by the Coy River. The increased altitude of the moun- 

 tains to the westward of the region drained by this river causes a dimin- 

 ished precipitation and more arid conditions here than prevail farther 



