PENNSYLVANIA ANORTHOSITES 
35 
culture of the region. This may be seen on the topographic map 
which shows that the circumference of the ellipsoidal anorthosite 
area, which is so clearly defined by the courses of the streams, is 
further accentuated by railroad lines and towns, all of which are 
confined to these stream valleys. The entire central area, higher 
and less accessible, is exclusively farm land. This upland interior 
is a water-shed from which small tributary streams radiate to the 
bordering main streams. At an altitude approximating 600 feet 
there is evidence of a break in the erosion cycle. Above this 
level the land rises gradually, while below, it dips steeply. This 
indicates accelerated stream-action following a period of retarda¬ 
tion. The surface above the 600 foot contour interval may repre¬ 
sent erosion during the Harrisburg cycle. This cycle was inter¬ 
rupted by uplift which renewed erosion and accelerated vertical 
cutting, producing the steeper slopes below the 600 foot contour. 
Erosion levels later than Harrisburg are not recognizable in the 
area of the anorthosite, where, with the exception just mentioned, 
no traces are preserved of the slight interruptions in erosion dur¬ 
ing late geological times. 
That portion of eastern Pennsylvania which is called the Pied¬ 
mont Province, was a part of the very ancient land-mass called 
Appalachia. In pre-Cambrian times this land-mass extended along 
the Atlantic border, its eastern limit reaching beyond the present 
shore-line, its western border submerged beneath the Appalachian 
sea. “Appalachia contributed the materials and the Appalachian 
Sea was the basin in which the materials were laid down in beds 
that ultimately, after they had been folded, uplifted, and eroded, 
formed the Appalachian Highlands.” (Bascom). 
The oldest of the pre-Cambrian rocks represented within the 
Honeybrook area are the Baltimore and the Pickering gneisses. 
Before the beginning of the Paleozoic era these sediments, which 
were laid down in the shallow waters of the Appalachian Sea, 
w’ere first metamorphosed during earth movements which were 
accompanied by intrusions of igneous material. In the Honey- 
brook region the masses of quartz-monzonite, anorthosite, gab- 
bro, pyroxenite, and peridotite belong to this period of intrusion. 
That a prolonged period of erosion followed this uplift, bringing 
about the removal of much of the sedimentary covering and ex¬ 
posing portions of these intrusives even before the close of pre- 
