of the Middle Atlantic Coast Region. 493 



Sunken River Channel in Chesapeake Bay. — As stated 

 above, if the theory of a recent subsidence of the Hudson 

 River is to be successfully maintained, a similar subsidence 

 must be proved for the Delaware and for Chesapeake Bay. It 

 must be confessed that for many years we have been searching 

 for sunken channels for those bays without finding them ; we 

 were looking for them in a wrong direction, outside of the 

 bays, instead of inside. We supposed Cape Henlopen and 

 Cape Henry occupied relative positions to those channels analo- 

 gous to that of Sandy Hook to the sunken Hudson River 

 channel ; we took the Coast-line as our line of departure in- 

 stead of taking the Fall-line. This line which is easily identi- 

 fied by the site of New York, Trenton, Philadelphia, Havre 

 de Grace, Baltimore,* Washington, etc., separates two widely 

 different geological regions, the region of crystalline and Trias- 

 sic rocks to the north and west from the stratified clays and 

 gravels to the south and east, and it must be assumed that any 

 seismic disturbance would affect these two regions unequally 

 and the coastal plain to a greater extent than the Piedmont 

 region. 



Now, the sinking of the land to the extent of 100 feet, let 

 us say fifty feet, would hardly affect the physiography of those 

 parts of the country above the hypsometrical line of fifty feet, 

 but all land below this level would be appropriated by the 

 waters and reached by the tides ; rivers with low shores would 

 be converted into bays or estuaries, those situated in rising 

 ground would have the lower parts of their valleys flooded, it 

 now remains for us to examine Delaware and Chesapeake Bays 

 for traces of deeper and narrower channels than those which 

 can be accounted for by existing conditions. 



Passing Delaware Bay, for reasons which will be explained 

 farther on, and turning to Chesapeake Bay, we readily find, 

 upon examining the soundings, a narrow and deep inner chan- 

 nel which can be traced nearly through the entire length of the 

 bay, from the mouth of Bush River to that of the Rappahan- 

 nock, a distance of 120 miles. In an average width of the bay 

 of ten miles, this channel commences with one mile's breadth 

 in its upper part, increasing to two miles near its southern 

 limit. The descent of the bottom of the bay is very gradual 

 from the shore until the depth of eight fathoms is passed, 

 when the bottom abruptly plunges to the depth of about 

 twenty fathoms (from fifteen to twenty-six fathoms). The 

 bathymetrical line of forty-eight feet may then be taken as the 

 limit of this inner deep channel. We subjoin four cross-sec- 

 tions of the bay, taken about thirty-five miles apart. It will 

 be seen that the areas of these sections are gradually increasing, 



Am. Jour. Sci.— Third Series, Yol. XLI, No. 246.— June, 1891. 

 33 



