Liwers of Northern New Jersey. 99 
stream hereabouts made so early a capture of adjacent superim- 
posed streams that all traces of their initial discordant courses 
have been obliterated by the development of structurally accor- 
dant subsequent streams. 
The Watchung ridges extend only about eight miles northward 
of the Paterson gaps, but reach thirty miles southwestward. It 
is therefore chiefly in the latter direction that we may expect to 
find examples of incomplete adjustment following superimposi- 
tion and capture. At Milburn, there is a deep gap in First moun- 
tain, and opposite this at Summit (S, fig. 1) a partly drift-filled 
gap in Second mountain: this I am disposed to regard as the 
former outlet of the Rockaway-Rahway river, which on account 
of its considerable size was not captured by the Passaic until it 
had cut its passage across the trap sheets almost to a safe depth. 
The diverted upper portion—the Rockaway—now joins the Pas- 
saic ; its crooked course from the Highlands via Boonton (Bn) 
being a post-glacial irregularity ; the beheaded lower portion— 
the Rahway—heads on the ridge of Second mountain, retains the 
pair of subsequent streams between the two ridges, and flows in 
diminished volume to the sea: the divide between the two por- 
tions being in its mature stable position on Second mountain. 
South of the Milburn gap, there are three streams that main- 
tain water gaps in First mountain, and five head branches of these 
three streams rise behind the crest of Second mountain. These 
must be interpreted as remnants of streams that once rose further 
inland, and whose upper courses have been captured by the vic- 
torious upper Passaic; but it is noteworthy that here, at the 
greatest distance from the gap of the master stream at Paterson, 
the divides between the diverted and beheaded portions of these 
southern streams should lie in unstable positions, back of the 
crest line of Second mountain. ‘This is exactly what the hypothe- 
sis of a superimposed origin for these streams would require ; and 
if the complexity of accordance between deduction and fact here 
presented be duly considered, I believe new confidence may be 
gained in the hypothesis of superimposition, already rendered 
likely from other evidence. 
The rectangular courses of the streams that cross First and 
Second mountains southwest of Milburn do not militate against 
their initial obliquely superimposed courses ; for, as Gilbert has 
shown, oblique courses across tilted beds, alternately hard and 
- soft, will gradually shift until they follow rectangular courses, 
