The National Geographic Magazine, Vol. I., No. 3, July, 1889Various
Science
The National Geographic Magazine, Vol. I., No. 3, July, 1889
Various
Geography -- Periodicals
Again, as far as present appearances go, we can give no
sufficient reason to explain why possession of the headwaters of the
Juniata was not gained by some subsequent stream of its own, such as G,
fig. 18, instead of by a side-stream of the river in the neighboring
syncline; but it may be admitted, on the other hand, that as far as we
can estimate the chances for conquest, there was nothing distinctly in
favor of one or the other of the side-streams concerned; and as long as
the problem is solved indifferently in favor of one or the other, we
may accept the lead of the facts and say that some control not now
apparent determined that the diversion should be, as drawn, through D
and not through G. The detailed location of the Juniata in its middle
course below Lewistown will be considered in a later section.
[Illustration: FIG. 22.]
[Illustration: FIG. 23.]
[Illustration: FIG. 24.]
30. _Avoidance of the Broad Top basin by the Juniata
headwaters_.--Another highly characteristic change that the Juniata has
suffered is revealed by examining the adjustments that would have taken
place in the general topography of the Broad Top district during the
Perm-Triassic cycle of erosion. When the basin, BT, fig. 22, was first
outlined, centripetal streams descended its slopes from all sides and
their waters accumulated as a lake in the center, overflowing to the
east into the subordinate basin, A, in the Juniata syncline along side
of the larger basin, and thence escaping northeast. In due time, the
breaching of the slopes opened the softer Devonian rocks beneath and
peripheral lowlands were opened on them. The process by which the
Juniata departed from its original axial location, J, fig. 22, to a
parallel course on the southeastern side of the syncline, J, fig. 23,
has been described (fig. 18). The subsequent changes are manifest. Some
lateral branch of the Juniata, like N, fig. 23, would work its way
around the northern end of the Broad Top canoe on the soft underlying
rocks and capture the axial stream, C, that came from the depression
between Nittany and Kishicoquillas highlands; thus reënforced, capture
would be made of a radial stream from the west, Tn, the existing Tyrone
branch of the Juniata; in a later stage the other streams of the
western side of the basin would be acquired, their divertor
constituting the Little Juniata of to-day; and the end would be when
the original Juniata, A, fig. 22, that once issued from the subordinate
synclinal as a large stream, had lost all its western tributaries, and
was but a shrunken beheaded remnant of a river, now seen in Aughwick
creek, A, fig. 24. In the meantime, the former lake basin was fast
becoming a synclinal mountain of diminishing perimeter. The only really
mysterious courses of the present streams are where the Little Juniata
runs in and out of the western border of the Broad Top synclinal, and
where the Frankstown (FT) branch of the Juniata maintains its
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