36 SEA AND LAND 



a ruined cave or chasm, or a few rolled pebbles, which have 

 been covered, and thus protected from cleca)'. b)- the talus of 

 angular fragments, which weathering action has drawn down 

 the cliffs. Here and there he may tind his evidence reduced 

 to that which is afforded by the existence of solitary steeps, 

 which were evidently islands in the open sea. Thus, on the 

 Piedmont IMain, to the east of the I^lue Ridge in Virginia and 

 ihe Carolinas, there are occasional detached elevations, rising 

 as hills or mountains from the level country, the origin of 

 which, on account of the steep faces of these elevations and 

 the nature of the accumulations at their base, we have to 

 believe to have been due to the fact that the\' were, in no 

 very ancient da)', islands lying off a shore which lay to the 

 westward. It may be noted in passing, that such detached 

 islands are often saved from destruction by the fact that the 

 waves and currents keep their bases free of pebbles and thus 

 remove the agents which, as we have seen, serve to batter 

 the bases of the cliffs. 



It is easy to see that the effacement of the ancient 

 indications of marine work depends upon the constant down- 

 wearing of the land, which is brought about by the agency 

 of sub-aerial decay, by the action of frost, and by the move- 

 ments of water in streams or glaciers. Although the amount 

 of this down-wearing is variable, it probably amounts to an 

 average of a foot in from three to six thousand years, so that 

 in a million years, not a long term in the geological sense, the 

 lantl surface descends some hundrc^d feet, or enough to take 

 away all the indices of an ordinary shore life. The fact that 

 such an escarpment hatl an original bold relief, would be 

 likely to cause the process of decay along its line to be much 

 accelerated. We, therefore, cannot expect this kind of record 



