TERRACES OF SHINGLE 



337 



deal of food, in case we should be snowed up, as the season was 

 rather late for passing the Portillo. 



Marcli igth. — We rode during this day to the last, and 

 therefore most elevated house in the valley. The number of 

 inhabitants became scanty ; 

 but wherever water could 

 be brought on the land, it 

 was very fertile. All the 

 main valleys in the Cordillera 

 are characterised by having, 

 on both sides, a fringe or 

 terrace of shingle and sand, 

 rudely stratified, and gener- 

 ally of considerable thickness. 

 These fringes evidently once 

 extended across the valleys, 

 and were united ; and the 

 bottoms of the valleys in 

 northern Chile, where there 

 are no streams, are thus 

 smoothly filled up. On these 

 fringes the roads are gener- 

 ally carried, for their surfaces 

 are even, and they rise with 

 a very gentle slope up the 

 valleys ; hence, also, they 

 are easily cultivated by 

 irrigation. They may be 

 traced up to a height of between 7000 and 9000 feet, 

 where they become hidden by the irregular piles of debris. 

 At the lower end or mouths of the valleys, they are 

 continuously united to those land-locked plains (also formed 

 of shingle) at the foot of the main Cordillera, which I 

 have described in a former chapter as characteristic of the 

 scenery of Chile, and which were undoubtedly deposited when 

 the sea penetrated Chile, as it now does the more southern 

 coasts. No one fact in the geology of South America inter- 

 ested me more than these terraces of rudely-stratified shingle. 

 They precisely resemble in composition the matter which the 

 torrents in each valley would deposit, if they were checked in 



z 



CHILENOS. 



