of the Middle Atlantic Coast Region. 495 



streams, whether an ellipse or parabola, the cross-section at 

 Wolf trap comes nearer to it than any of the preceding ones 

 and no combination of circumstances, no shifting or turning of 

 channel can satisfactorily explain, as a purely tidal phenomenon, 

 the existence of the deep incisions at the bottom of the cross- 

 sections. We are forced to conclude that these incisions are 

 due to pre-existing conditions, that they show the former chan- 

 nel of a river at a time when the whole region lay about forty- 

 eight feet higher than at present, when Chesapeake Bay did 

 not exist, but when the Susquehanna was at least 150 miles 

 longer than at present (rather more than the submerged Hudson) 

 and gathered upon its way to the sea the waters of the Patuxent, 

 Potomac and Rappahannock. The reason that we cannot trace 

 the channel farther up the bay than Bush Piver and to the 

 mouth of the Susquehanna is, no doubt, owing to the fact 

 that the Susquehanna has filled up the upper part of its old 

 channel, for which it has no further use, with its sediment ; 

 and the borings to a depth of 140 feet at Fishing Battery, 

 below Havre de Grace, through alluvium, which Mr. McGee 

 reports,* quite favor such a supposition. As stated above, the 

 channel disappears below the mouth of the Pappahannock 

 with a depth of about fifty feet. I am not prepared now to 

 answer the question, whether the bar and actual end of the 

 old river is here or whether there is but a temporary interrup- 

 tion of the channel by subsequent deposits from rivers empty- 

 ing into the bay. The answer is not material to the present 

 inquiry. The river channel appears to have hugged its eastern 

 shore, which in several places appears to have risen into bluffs, 

 from 15 to 25 feet high, while the western shore was low and. 

 marshy. The soundings in the bay are not the only indica- 

 tions of a depression ; they can be found everywhere along 

 the shores of the bay, even by a mere inspection of the charts. 

 It is entirely beyond the ability of the present sluggish streams 

 to have eroded their channels to the great width which is so 

 characteristic of the lower part of all streams entering the 

 Chesapeake. The absence of deltas and bars at the mouths of 

 the rivers, the almost total absence of drainage-area for a long 

 strip of the western shore of the bay above the Pappahannock, 

 all are suggestive of subsidence, in fact have been commented 

 upon in this direction by Mr. McGee in his exhaustive study 

 of the Geology of Chesapeake Bay.f On more than one occa- 

 sion he speaks of the drowned rivers of the bay. 



There is another way in which we may arrive at an estimate of 

 the probable amount of subsidence. The profile given (p. 494) 

 of the Susquehanna Piver at the crossing of the Baltimore and 



* Seventh Annual Report U. S. Geological Survey, p. r>80. 



f Seventh Annual Report, U. S. Geological Survey, pp. 537-646. 



