The National Geographic Magazine, Vol. II., No. 2, May, 1890Various
Science
The National Geographic Magazine, Vol. II., No. 2, May, 1890
Various
Geography -- Periodicals
The only method now known by which these several doubly transverse
streams could have been established in the not too distant past, is by
superimposition from the Cretaceous cover that was laid upon the old
Schooley peneplain. It has already been stated that when the Highlands
and this region together had been nearly baselevelled, the coastal
portion of the resulting peneplain was submerged and buried by an
unconformable cover of waste derived from the non-submerged portion:
hence when the whole area was lifted to something like its present
height, a new system of consequent streams was born on the revealed sea
bottom. Since then, time enough may have passed to allow the streams to
sink their channels through the unconformable cover and strip it off,
and thus superimpose themselves on the Triassic rocks below: we should
therefore find them, in so far as they have not yet been re-adjusted,
following inconsequent, discordant courses on the under formation. The
existing overlap of the Cretaceous beds on the still buried Triassic
portion of the old Schooley peneplain makes it evident that such an
origin for the Watchung streams is possible; but it has not yet been
independently proved that the Cretaceous cover ever reached so far
inland as to cross the Watchung ridges.
Want of other explanation for the Watchung streams is not satisfactory
evidence in favor of the explanation here suggested. There should be
external evidence that the Triassic area has actually been submerged
and buried after it was baselevelled to the Schooley peneplain and
before it was uplifted to its present altitude; other streams as well
as the ones thus far indicated, should bear signs of superimposition;
and if adjustment of the superimposed courses has begun, it should be
systematically carried farthest near the largest streams. I shall not
here state more than in brief form, the sufficient evidence that can be
quoted in favor of the first and second requisites. Suffice it to say
that the overlap of the Cretaceous beds (which contain practically no
Triassic fragments) on the bevelled Triassic strata at Amboy and
elsewhere indicates submergence after baselevelling; and that the
pebbles, sands and marls of the Cretaceous series point clearly to the
Highlands as their source. The submergence must therefore have reached
inland across the Triassic formation at least to the margin of the
crystalline rocks. Some shore-line cutting must have been done at the
margin of the Highlands during Cretaceous time, but the generally
rolling surface of the old peneplain leads me to ascribe its origin
chiefly to subaërial wasting. Moreover, the North Branch of the
Raritan, between Mendham and Peapack (* Fig. 1) and the Lockatong (L),
a small branch of the Delaware on the West Hunterdon sandstone plateau,
give striking indications of superimposition in the discordance of
their courses with the weaker structural lines of their basins, so
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account