90 National Geographic Magazine. 
less complete and of briefer duration than these three. There is 
the tilted and deeply eroded peneplain of the Highlands, whose 
initial form may be called the Schooley peneplain, from the dis- 
tinct exhibition of one of its remnants on Schooley’s mountain ; 
this was the product of Jurassic and Cretaceous denudation. There 
is the younger central baselevelled plain, developed during 
Tertiary time, or thereabouts, on the weaker Triassic and Creta- 
ceous beds; and the associated valleys of the same age that have 
been sunk into the weakest rocks of the Highlands. There are 
the shallow valleys in the Central plain, of the latest post-tertiary 
cycle, requiring the name of this region to be changed from 
plain, as it was lately, to pastplain, as it. is now. ‘The first cycle, 
in which the Schooley peneplain was produced, witnessed the 
accomplishment of a great work; it included in its later part, 
besides various other oscillations, the sub-cycle when the seaward 
or southeastern part of the peneplain was gently submerged and 
buried to a sight depth under Cretaceous deposits. The second 
cycle was shorter; being a time sufficient to baselevel the softer 
beds, but not seriously to consume the harder parts of the pre- 
existing surface. We are still in the third cycle, of which but 
asmall part has elapsed. The question with which this essay 
opened may now be taken up. i 
The streams and rivers of northern New Jersey may be 
examined, with the intention of classifying them according to 
their conditions of origin, to their degree of complexity as indi- 
cated by the number of geographic. cycles through which they 
have lived, and to the advance made toward their mature ade 
ment. 
The Musconetcong may be taken as the type of the Highland 
streams. It flows southwestward along a narrow limestone val- 
ley between crystalline plateaus on either side, entering the 
Delaware a little below Easton, Pa., (E, fig. 1). It drains a 
country that has been enormously denuded, and during the Jura- 
Cretaceous cycle of this deep denudation, there must have been 
time for it and its fellows to become thoroughly adjusted to the 
structure of the region; it must be chiefly for this reason that it 
flows so closely along the weak limestone belt, and has its divides 
close by on the adjoining harder crystallines, (M, fig. 2). What- 
ever its origin, it has lost every initial feature that was discordant 
with the deep structures that it discovered beneath the initial 
Surface ; it is maturely adjusted to its environment. It endured 
