260 Gravel-Terraces of Coqiiimbo past n. 



conquered by the elevatory movement, as often as it 

 recommences, at about the same period ; and hence the 

 terraces, or accumulated beach-lines, will commence 

 being formed at nearly the same levels : at each suc- 

 ceeding period of rest, they will, also, be eaten into at 

 nearly the same rate, and consequently there will be a 

 much closer coincidence in their levels and inclinations, 

 than in the terraces and escarpments formed round 

 bays with their different parts very differently exposed 

 to the action of the sea. It is only where the waves 

 are enabled, after a long lapse of time, slowly to corrode 

 hard rocks, or to throw up, owing to the supply of 

 sediment being small and to the surface being steeply 

 inclined, a narrow beach or mound, that we can expect, 

 as at Glen Eoy in Scotland, 1 a distinct line marking an 

 old sea-level, and which will be strictly horizontal , if 

 the subsequent elevatory movements have been so : for 

 in these cases no discernible effects will be produced, 

 except during the long intervening periods of rest; 

 whereas in the case of step-formed coasts, such as those 

 described in this and the preceding chapter, the terraces 

 themselves are accumulated during the slow elevatory 

 process, the accumulation commencing sooner in pro- 

 tected than in exposed situations, and sooner where 

 there is copious supply of detritus than where there is 

 little ; on the other hand, the steps or escarpments are 

 formed during the stationary periods, and are more 

 deeply cut down and into the coast-land, in exposed 

 than in protected situations ; — the cutting action, more- 

 over, being prolonged in the most exposed parts, both 

 during the beginning and ending, if slow, of the upward 

 movement. 



Although in the foregoing discussion I have assumed 

 the elevation to have been horizontal, it may be sus- 

 1 ' Philosophical Transactions/ 1S39, p. 39. 



