chap. ix. not Horizontal. 259 



which, consequently, will be left standing higher and 

 higher above its level ; whilst at the still exposed mouth, 

 it might well happen that the waves might be enabled 

 to cut deeper and deeper, both down and into the cliffs, 

 as the land slowly rose. 



The greater or lesser destroying power of the waves 

 at the mouths of successive bays, comparatively with 

 this same power in their upper and protected parts, will 

 vary as the bays become changed in form and size, and 

 therefore at different levels, at their mouths and heads, 

 more or less of the surfaces between the escarpments, 

 (that is, the accumulated beach-lines or terraces) will 

 be left undestroyed : from what has gone before we can 

 see that, according as the elevatory movements after 

 each cessation recommence more or less slowly, according 

 to the amount of detritus delivered by the river at the 

 heads of the successive bays, and according to the degree 

 of protection afforded by their altered forms, so will a 

 greater or less extent of terrace be accumulated in the 

 upper part, to which there will be no surface at a cor- 

 responding level at the mouth : hence we can perceive 

 why no one terrace, taken in its whole breadth and 

 followed up the valley, is horizontal, v though each 

 separate beach-line must have been so ; and why the 

 inclination of the several terraces, both transversely, 

 and longitudinally up the valley, is not alike. 



I have entered into this case in some detail, for I 

 was long perplexed (and others have felt the same 

 difficulty) in understanding how, on the idea of an 

 equable elevation with the sea at intervals eating into 

 the land, it came that neither the terraces nor the upper 

 nor lower edges of the escarpments were horizontal. 

 Along lines of coast, even of great lengths, such as that 

 of Patagonia, if they are nearly uniformly exposed, the 

 corroding power of the waves will be checked and 



