Davis and Wood.] 
404 
[Nov 20, 
29. Drainage of the Watchung Crescent. Many of the streams 
that took courses across the Cretaceous cover of the submerged por- 
tion of the Schooley peneplain soon encountered the buried edges 
of hard trap ridges beneath the soft Cretaceous beds and from this 
time forward there was frequent opportunity for one stream to rob 
another and to become confirmed in this habit of robbery as time 
went on. To illustrate this, suppose the land were raised some 
two hundred feet higher than it now is. The Raritan would then 
soon encounter the Palisades-Roeky Hill trap sheet, fig. 1, under 
the Cretaceous beds below New Brunswick ; being a large river, 
it would with relative quickness cut a deep gorge or gap through 
atlie resistant sheet. But the smaller Rahway river, encountering 
;the same obstruction a little farther north, would be so slow in ent- 
iling down its gap that, before it was safely trenched close to base- 
level, some side branch of the Raritan, such as Bound Brook, 
would eat its way back and tap the headwaters of the Rahway and 
lead them away by the deeper passage prepared by the larger river. 
Thus strengthened, the Raritan would be still better enabled to 
perform the same piratic act on other rivers, and hence the number 
of streams that cross the trap sheet would be lessened and at last 
reduced to a small number at the time of mature adjustment. Is 
it not likely that some such process as this is to be considered in 
explaining the present course of the streams in the region of the 
curved Watchung mountains? In the discussion of this problem, 
we must refer to fig. 12, which is reduced from a tracing of the re- 
gion from the relief map of the state. 1 
We have concluded that the Cretaceous cover once stretched 
over the Watchung ridges when they made but faint relief on the 
old Schooley peneplain. The streams born on the newly elevated 
and gently sloping Cretaceous cover cannot be thought to have 
taken courses as circuitous as these that now lead the drainage out 
from the Highlands. It is true that part of the present complexity 
is certainly due to obstructions by glacial drift: for example, the 
round-about outlet of Great Swamp is pretty surely determined by 
the great morainic barrier, stretching from Morristown to Chatham 
and traversing the Triassic lowland that had in Somerville time 
i The Highland plateau in fig. 12 is separated from the Triassic lowland by a line of 
heavy dots. The fine dotted line is the contour of thi’ee hundred feet; the heavier 
broken line of five hundred feet. The several parts of the three trap ridges composing 
the Watchung mountains are marked I, II and III. Several cities and towns are abbre- 
viated thus; B. Br., Bound Brook; Bn., Boonton; Mu., Morristown; N. Br., New 
Brunswick; Pat.,. Pater-son. 
