Davis and Wood.] 
414 
[Nov. 20, 
by the “new route/’ he must notice the little-stream valleys that in- 
terrupt the general interstream plain between Trenton and Bound 
Brook. These are all the product of the Millstone cycle. The 
valleys are of moderate width, and hence this cycle is not far ad- 
vanced. 
The depth to which a stream may cut its channel depends on the 
altitude of its drainage area above its baselevel. Lowlands can 
therefore never acquire the intensity of topographic relief that 
characterizes the maturer stage of highlands. It is for this reason 
that the valleys that have been cut in different parts of the Central 
plain are of different depths. The valleys of the Delaware and 
Lehigh, above mentioned, are much deeper than the valley of the 
Raritan at New Brunswick ; not because the former are older, but 
because they have had a higher mass in which their trenches were 
to be cut. So again with the Raritan at New Brunswick and at 
Bound Brook ; the stream has insignificant fall from one place to 
the other, but its trench deepens from fifty feet below the Cen- 
tral plain at Bound Brook to a hundred and thirty feet below it 
at New Brunswick, because the surface that it trenches rises in 
that direction. The Millstone river, fig. 14, 1 after which the cy- 
cle under discussion is named, is even more interesting in this re- 
spect. Its various head branches rise in the Cretaceous plain, 
where their trenches are sunk from twenty to forty feet below the 
general interstream surface ; the streams thus cross the depressed 
portion of the plain south of Princeton, and then uniting into a 
single river they enter the higher part of the plain northwest of the 
fall-line, here cutting a valley a hundred feet deeper than before, 
because the plain is now a hundred feet higher;’ but the depth de- 
creases as the river crosses the Triassic plain to its northwestern 
lower side, and in the neighborhood of the town of Millstone, the 
stream is about fifty feet below the plain, like the Raritan which 
the Millstone there joins. The headwaters of the Millstone have 
not yet had time to sink their channels close to baselevel ; for their 
discharge to the sea is by a long roundabout course by which their 
slope is decreased ; and on the way their outlet stream crosses the 
hard trap sheet of Rocky Hill, where the deepening of the channel 
is retarded. In contrast with the delayed deepening of these head- 
•Fig. 14 includes the drainage of the Millstone river : BB, Bound Brook; C, Clarkes- 
burg; J, Jamesburg; N. Br., New Brunswick; Pr., Princeton; S, Somerville. The fall 
line is dotted from Trenton to Lawrence Brook. 
