314 SHINGLE TERRACES. [chap. xv. 



where there are no streams, are thus smoothly filled up. 

 On these fringes the roads are generally 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, when they become hidden by the 

 irregular piles of debt is. 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 interested 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 their 

 course by any cause, such as entering a lake or arm of the 

 sea ; < but the torrents, instead of depositing matter, are now 

 steadily at work wearing away both the solid rock and 

 these alluvial deposits, along the whole line of every main 

 valley and side valley. It is impossible here to give the 

 reasons, but I am convinced that the shingle terraces were 

 accumulated during the gradual elevation of the Cordillera, 

 by the torrents delivering, at successive levels, their detritus 

 on the beach-heads of long narrow arms of the sea, first 

 high up the valleys, then lower and lower down as the 

 land slowly rose. If this be so, and I cannot doubt it, the 

 grand and broken chain of the Cordillera, instead of having 

 been suddenly thrown up, as was till lately the universal, 

 and still is the common opinion of geologists, has been 

 slowly upheaved in mass, in the same gradual manner as 

 the coasts of the Atlantic and Pacific have risen within the 

 recent period. A multitude of facts in the structure of the 

 Cordillera, on this view, receive a simple explanation. 



The rivers which flow in these valleys ought rather to be 

 called mountain-torrents. Their inclination is very great, 

 and their water the colour of mud. The roar which the 

 Maypu made, as it rushed over the great rounded frag- 

 ments, was like that of the sea. Amidst the din of rushing 

 waters, the noise from the stones, as they rattled one over 

 another, was most distinctly audible even from a distance. 

 This rattling noise, night and day, may be heard along the 

 whole course of the torrent. The sound spoke eloquently 



