chap. ix. and Action of Sea on the Laiid. 281 



breadth and height, and the present period is not one 

 of rest in the elevation and of contingent denudation ; 

 but if the rising be not prolonged at a quick rate, there 

 is every probability that the sea will soon regain its 

 former horizontal limits. I observed similar low slop- 

 ing fringes on several parts of the coast, both northward 

 of Valparaiso and near Coquimbo ; but at this latter 

 place, from the change in form which the coast has 

 undergone since the old escarpments were worn, it may 

 be doubted whether the sea, acting for any length of 

 time at its present level, would eat into the land ; for 

 it now rather tends to throw up great masses of sand. 

 It is from facts such as these that I have generally used 

 the term comparative rest, as applied to the elevation 

 of the land ; the rest or cessation in the movement 

 being comparative both with what has preceded it and 

 followed it, and with the sea's power of corrosion at 

 each spot and at each level. Near Lima, the cliff- 

 formed shores of San Lorenzo, and on the mainland 

 south of Callao, show that the sea is gaining on the 

 land ; and as we have here some evidence that its 

 surface has lately subsided or is still sinking, the periods 

 of comparative rest in the elevation and of contingent 

 denudation, may probably in many cases include periods 

 of subsidence. It is only, as was shown in detail when 

 discussing the terraces of Coquimbo, when the sea with 

 difficulty and after a long lapse of time has either 

 corroded a narrow ledge into solid rock, or has heaped 

 up on a steep surface a narrow mound of detritus, that 

 we can confidently assert that the land at that level and 

 at that period long remained absolutely stationary. In 

 the case of terraces formed of gravel or sand, although 

 the elevation may have been strictly horizontal, it may 

 well happen that no one level beach-line may be trace- 

 able, and that neither the terraces themselves nor the 



