chap. x. their Marine Origin. 295 



the most abrupt bends. To suppose that as the land 

 now stands, the rivers deposited the shingle along the 

 course of every . valley, and all their main branches, 

 appears to me preposterous, seeing that these same 

 rivers not only are now removing and have removed 

 much of this deposit, but are everywhere tending to cut 

 deep and narrow gorges in the hard underlying rocks. 



I have stated that these fringes of gravel, the origin 

 of which is inexplicable on the notion of debacles or 

 of ordinary alluvial action, are directly continuous with 

 the similarly-composed basin-like plains at the foot of 

 the Cordillera, which, from the several reasons before 

 assigned, I cannot doubt were modelled by the agency 

 of the sea. Now if we suppose that the sea formerly 

 occupied the valleys of the Chilian Cordillera, in pre- 

 cisely the same manner as it now does in the more 

 southern parts of the continent, where deep winding 

 creeks penetrate into the very heart of, and in the case 

 of Obstruction Sound quite through, this great range ; 

 and if we suppose that the mountains were upraised in 

 the same slow manner as the eastern and western coasts 

 have been upraised within the recent period, then the 

 origin and formation of these sloping, terrace-like fringes 

 of gravel can be simply explained. For every part of 

 the bottom of each valley will, on this view, have long 

 stood at the head of a sea-creek, into which the then 

 existing torrents will have delivered fragments of rocks, 

 where, by the action of the tides, they will have been 

 rolled, sometimes encrusted, rudely stratified, and the 

 whole surface levelled by the blending together of the 

 successive beach lines. 1 As the land rose, the torrents 



1 Sloping terraces of precisely similar structure have been de- 

 scribed by me (' Philosopb. Transactions,' 1839, p. 58) in the valleys 

 of Lochaber in Scotland, where, at higher levels, the parallel roads 

 of Glen Eoy show the marks of the long and quiet residence of a 

 glacial lake. I bave no doubt that sloping terraces would have been 



