286 Basin-like Plains of Chile. paet n. 



watersheds, is directed towards three openings in the 

 encircling mountains. 1 The streams flowing from the 

 three southern basin-like plains, after passing through 

 the breaches to the west, unite and form the river 

 Rapel, which enters the Pacific near Navidad. I 

 followed the southernmost branch of this river, and 

 found that the basin or plain of S. Fernando is con- 

 tinuously and smoothly united with those plains, 

 which were described in the ninth chapter, as being 

 worn near the coast into successive cave-eaten escarp- 

 ments, and still nearer to the coast, as being strewed with 

 upraised recent marine remains. 



I might have given descriptions of numerous other 

 plains of the same general form, some at the foot of 

 the Cordillera, some near the coast, and some half-way 

 between these points." I will allude only to one other, 

 namely, the plain of Uspallata, lying on the eastern 

 or opposite side of the Cordillera, between that great 

 range and the parallel lower range of Uspallata. 

 According to Miers, its surface is 6,000 feet above the 

 level of the sea : it is from ten to fifteen miles in 

 width, and is said to extend with an unbroken surface 

 for 180 miles northwards: it is drained by two rivers 

 passing through breaches in the mountains to the east. 

 On the banks of the R. Mendoza it is seen to be 

 composed of a great accumulation of stratified shingle, 

 estimated at 400 feet in thickness. In general appear- 

 ance, and in numerous points of structure, this plain 

 closely resembles those of Chile. 



The origin and manner of formation of the thick 

 beds of gravel, sandy clay, volcanic detritus, and cal- 

 careous tuff, composing these basin-like plains, is very 



1 It appears from Capt. Herbert's account of the Diluvium of the 

 Himalaya ('Gleanings of Science,' Calcutta, vol. ii. p. 164), that 

 precisely similar remarks apply to the drainage of the plains or 

 valleys between those great mountains. 



