PENNSYLVANIA ANORTHOSITES 
39 
The igneous materials intruded during the pre-Cambrian earth- 
movements which lifted and folded the Baltimore and the Picker¬ 
ing sedimentaries accumulated upon western Appalachia, and 
were themselves subjected later to pressure and metamorphism at 
three different times. At the close of the Ordovicic period both 
sedimentary and igneous rocks probably suffered uplift and slight 
folding. Again, from Mid-Devonic through to the close of Car¬ 
bonic times they were subjected to severe and more or less con¬ 
tinuous earth-movements with close-folding and faulting, which 
resulted in the recrystallization of the Cambric, Cambro-Ordovicic 
and Ordovicic sediments into quartzites and quartz-schists, cal¬ 
careous schists and marbles, and mica schists, respectively, and. 
brought about the conversion of the pre-Cambrian intrusives into 
orthogneisses. Later, toward the close of the Triassic period, 
earth-movements contemporaneous with the intrusion and extru¬ 
sion of igneous material produced further metamorphism through¬ 
out the region. During the prolonged erosion interval from 
Triassic time to the Present, thousands of feet of Paleozoic sedi¬ 
ments were removed. In the Honeybrook area, the great folds 
of the Cambric quartzites and Cambro-Ordovicic limestones ap¬ 
pear for the most part only as narrow, alternating ridges and val¬ 
leys which are the roots of closely compressed anticlines and syn¬ 
clines trending northeast and southwest. These longitudinal belts 
of the Paleozoics are separated from one another by broad inter¬ 
vening areas of pre-Cambrian sedimentary and igneous rocks. 
The anorthosite and associated rocks are found in about the centre 
of the northern area of pre-Cambrian intrusives. 
The anorthosite mass is found in contact with quartz-monzonite 
except where, along the southern margin, a fault brings up the 
Cambric quartizites against it. The anorthosite may be readily 
distinguished from the surrounding rocks because of its grayish- 
blue color and its characteristic weathering. The color is due to 
the development of a secondary mineral, zoisite, which almost 
entirely replaces the original feldspathic constituent. The weath¬ 
ering is spheroidal, the fields being strewn with large, well-rounded, 
light grayish-blue, tough boulders, which are smooth-surfaced ow¬ 
ing to the uniformity of composition of the rock. The dark-col¬ 
ord, oxidized surfaces of the weathered quartz-monzonite, on 
the other hand, are rough and pitted, and the rock is easily crum- 
