DISCUSSION OF EVIDENCES OF CHANGES OF SEALP:VEL. 151 



on tlie elevated coastlines to the west of the Dismal swanij), in Viroinia 

 and North Carolina, I have found some traces of these barrier features, 

 and although I have suspected that the remnants of such to])ography 

 accounts for the formation of some high lying s\vami)s in certain of the 

 southern states of this country, it is evident that this group of coastal 

 structures is not to be trusted as evidence of old shorelines. Their pre- 

 vailing absence where they might be fairly ex[)ected to occur is perhaps 

 ilue to the fact that they are com})osed of almost pure sand, and thus do 

 not readily become occupied by vegetation. We readily perceive that 

 wherever along the coastline such sands cease to be fed from the sea they 

 are speedily dissii)ated by the wind. The same fate probably overtakes 

 them when they are elevated above their original plane of the coastline 

 on which they were formed. 



Character of dctrital Shore-beds. — The condition of the fragments which 

 make up the detrital beds of sea-margins affords an important indication 

 which may be used in determining elevated beaches. Where there are 

 pebbles which are the product of waVe-action, the condition of the 

 fragments affords an excellent basis for discrimination. The peculiar 

 movement of the detritus on a shore where rolling beaches occur brings 

 about the formation of sub-ovate pebbles, such as I have never been 

 able to find formed by any other mode of action except that used in the 

 revolving drums which serve for making boys' marbles. The nearest 

 approach to the result is attained by the subglacial streams which often 

 produce well rounded bits, yet the most of these differ notably from true 

 wave-worn pebbles. 



Remains of marine Scarfs. — Where it is possible to find a trace of a 

 scarf, however obscure, provided the remains be at coincident heights for 

 a considerable horizontal distance and along with this evidence remains 

 of a shelf containing rounded pebbles, the presumption that the indica- 

 tions are th(jse of a coastline is very strong. If by chance remnants of 

 caverns can Ijc found in the escarptnent, the association of proof becomes 

 yet stronger. 



Exposed oJf'^Jiore Deposits. — It might ])e sup])Ose(l that wherever in rela- 

 tively recent times a ])each now elevated has l)eon formed tlie surface of 

 the earth ])ol()\v its level would retain some indications that it liad ])een 

 beneath the water. It might reasonably be exi)ected that a submergence 

 which had endured long enough to permit the formation of characteristic 

 beach accumulation would have sufHced for the formation of a tolerabl 

 enduring marine deposit lying offshore. 



At the outset of my studies of the elevated beaches of the Atlantic 

 coast, the remains of which are of a rather fragmentary nature, I was led 

 to doul)t the verity of the indications by the absence of these marine 



