Pennsylvania Geology Final Report Volume 1 1981

66 GEOLOGICAL SURVEY OF PENNSYLVANIA.
The Pennsylvania Highlands.
Such is the lesson taught by the survey of the New-
Jersey highlands; and it is repeated by the survey of the
same belt in its extension in Pennsylvania. All that has
been said by Prof, Cook of the New Jersey azoic rocks, is
confirmed by Mr. D'Invilliers in his report on the azoic
rocks of Berks county, described in his Report of Progress
D3, Vol. IT, 1883, pages 49 to 57.
These Pennsylvania highlands also have been instru-
mentally surveyed and mapped in contour curves on a large
scale (1,600 feet to one inch) and published (on 16 sheets),
in an atlas to accompany Reports D2, D3 ; with a geologically-colored
index map (on one sheet), on a reduced scale
(2 miles to an inch) showing :— the ridges of gneiss, both
parallel and irregular ;—the patches of sedimentary sandstone
which once spread in a continuous sheet over the
whole of them ;— the limestone valleys north and south of
them ;—and the isolated limestone vales between them,
proving that the limestone formation also once spread continuously
over the whole region. Of these facts more will
be said hereafter in narrating the history of the sedimentary
formations. At present we are only concerned with the
Azoic mountain ridges themselves, and the nature of the
crystalline rocks of which they are composed, concerning
which the following statements may be confidently made :
1. The Pennsylvania highlands make an Azoic belt, of
irregular width, in a W. S. W. direction from the Delaware
to the Schuylkill, south of the Lehigh river, Bnt iso-
lated, short, small ridges rise through the overlying sandstone
and limestone strata north of the Lehigh river, showing
that the Azoic fioor extends underground under middle
and northern Pennsylvania, as it does under New York.
2. The sheet maps plainly exhibit an oblique arrangement
of N. E. and S. W. bearing subordinate ridges ; and
the limestone vales of the belt conform rather to this direc-
tion than to that of the belt as a whole. This oblique ten-
dency, however, seems to belong to the more ancient folding
of the Azoic rocks rather than to the later movements