450 J. f. NEWSOM 
to the strike of the rocks, and also to the upper and lower con- 
tacts of the particular group of strata formed, though several 
miles removed from either of those contacts. 
On the other hand, a stream flowing parallel with the contact 
and not far removed from it might cut down completely through 
the series of strata by which its course was originally determined, 
and reach the older underlying rocks. Under such circum- 
stances the newer beds through and along the edges of which 
the stream originally flowed, would in time be removed by 
erosion for some considerable distance from the line of contact, 
as shown in Fig. 4. 
It is, of course, difficult to point with certainty to streams 
at present far inland that have had their courses originally 
determined in the manner suggested. This explanation offers 
itself, however, for streams that now flow parallel to and in the 
neighborhood of contacts between sets of beds of different ages, 
as also for streams flowing parallel to preéxisting coast lines. 
It is not improbable that many streams flowing with the strike 
of strata, and whose courses have been attributed to stream 
capture, owe these courses to the simple fact of their having 
been primarily established in that position as here suggested. 
Many such streams may be seen on any detailed geologic and 
drainage map of our eastern and southern coastal region, though 
they are by no means limited to such regions. 
This explanation is suggested as a probable one in account- 
ing for the sudden southwest deflection of the Delaware River 
at Bordentown, N. J., and the Potomac near Washington, and 
for the sudden turn of the Susquehanna into the upper portion 
of Chesapeake Bay, which may be considered as its exten- 
sion. 
The same explanation is suggested also in, regard to the 
Tennessee River for the lower portion of its course where it 
flows northward through west Tennessee and Kentucky. 
Black River, in Arkansas, flows for almost its entire length 
near the line of contact between Tertiary and Paleozoic rocks. 
This stream may have had its course originally established, 
