of the Middle Atlantic Coast Region. 491 



ocean at the time when its feeder was yet an actual river 

 channel. 



The presence of clay on the bottom of the channels and on 

 the slopes, and its absence elsewhere, was assumed to furnish 

 proof for the assumption that this clay was not a mere super- 

 ficial covering, but that it is formed in situ and gives indica- 

 tions of strata in correlation with the Tertiary exposed towards 

 the northeast at Gay Head, as well as with that of New Jersey, 

 bearing west. 



The first one of these propositions, the one which accounts 

 for the sunken river channel, is the most important and 

 perhaps the most vulnerable one, and requires proof of the 

 following corollaries : 



1st. The shape and dimensions of the channel must accord 

 with those which should be assigned to a hypothetical river of 

 the size of the Hudson. ■ 



2d. Tidal and other currents now in existence cannot have 

 produced the channel. 



3d. A similar subsidence which must not necessarily be of 

 the same amount, must be proved for the nearest rivers to the 

 south, for the Delaware, Susquehanna (or Chesapeake) and 

 Potomac. (The rivers to the north may be left untouched 

 since Professor Dana has investigated the subject and recorded 

 the results in his paper on Long Island Sound in the Quaternary, 

 etc., mentioned above.) 



4th. It must be shown that diluvial deposits do not lie con- 

 formably on the surface of these channels but are eroded by 

 them, and all deposits found in the channels must be of alluvial 

 character. 



1. Size and shape of the Sub-marine Hudson River 

 Channel. — The breadth of the channel is about one and a 

 quarter miles, about the same as that of the river above the 

 Narrows. From New York City to the Dunderberg the chan- 

 nel is about three-quarters of a mile wide. These dimensions 

 tally well with the conditions expected from an ordinary tidal 

 stream, i. e. increased capacity with nearer approach to sea. 

 The main slope of the banks is 1°. This is less than we 

 expect of living rivers, but we should take into consideration 

 that, apart from currents, the corrasive action of sea water is 

 constantly engaged upon the work of destruction. It is rather 

 a matter of surprise to those who are familiar with the little 

 power of resistance of clay banks in sub-aerial exposure when 

 unprotected by gravel ledges or turf, that such banks should 

 be preserved at all under the sea. No special reason can be 

 assigned for the peculiarity that the river should first flow 

 fifteen miles to the south before turning east unless we assume 

 that it follows the fashion set by its neighboring rivers, the 



