338 



PORTILLO PASS 



CHAP. 



their course by an)" cause, such as entering" a hike or arm ot the 

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

 steadily at work wearing away both the sohd rock and these 

 alhivial deposits, along the \\-hole line of e\'er3' 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, b)' 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 



lUTH AML-.kl 



cannot doubt it, the grand and broken chain of the Cordillera, 

 instead of having been suddenh' 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 rcceix e a simple explanation. 



The rivers which flow in these \alleys 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 fragments, was like that of 

 the sea. Amidst the din of rushing waters, the noise from the 



