BASCOM.] ORES. 25 
The basic rock, by reason of its softer character, is more subject to 
alteration under dynamic action than are the hard acid rocks. The 
effect of this is seen in the almost universal schistosity of the basic 
rock. This metamorphism is accompanied by a correspondingly greater 
chemical alteration than is shown by the acid rocks. The alteration 
consists largely in the abundant development of epidote and chlorite, 
which gives to the rock its uniform green color and its popular name of 
" greenstone." 
Previous descriptions. — Dr. Hayden 1 notes the remarkable develop- 
ment of epidote as follows: 
Most beautiful epidote, with green and other shades of copper scattered in quartz. 
The blue is prevalent. Abundant in Blue Ridge. * * * 
Quartz and epidote. with green carbonate and red oxid of copper and native 
copper. Blue Ridge; abundant. 
The greenstones are locally known as the "copper rock," because of 
the copper ore which they carry. They are Rogers's "lower Primal 
slates," which "are highly indurated, and even decidedly crystalline, 
containing in some of their layers segregated specks, and even half- 
formed geodes [amygdules] of epidote and other minerals." "A highly 
altered, greenish slate." " Dark-green slate, with its epidote and 
white, intrusive quartz." Tyson describes them as " slates." Dr. Frazer 
calls them u chlorite schists," and Dr. Hunt terms them epidotic or 
chloritic rocks. Blandy approaches most nearly the present idea of 
their nature in describing them as "amygdaloidal trap." 
ORE DEPOSITS OF THE MONTEREY DISTRICT. 
The workable deposits of ore in the South Mountain fall into two 
lasses : The limonite ores, which are deposited in Paleozoic sedimeut- 
iry rocks, and the copper ores, which are associated with pre-Paleozoic 
gneous rocks. 
Profitable limonite iron mines are being worked at various localities 
n the South Mountain, in the Cambrian sandstone, and along the con- 
tacts between it and the Silurian limestone. They are fully discussed 
n the Final Report of the Second Geological Survey of Pennsylvania, 
Vo\. I. 
One such ore bank occurs within the Monterey district, on its north- 
astern boundary, at the contact between Triassic limestone and the 
Jambrian sandstone, near Old Maria furnace. This bank is exhausted 
ind has not been worked for many years. 
An interesting occurrence of copper ore and native copper 2 is to be 
bund within the South Mountain chain, in a belt extending from a 
mint some 6 miles north of the State line, in a southwesterly direction, 
'Loc.cit.,1822, p. 255. 
2 Frazer, Copper ores of Pennsylvania: Polytechnic Review, Vol. Ill, 1887, No. 16, p. 159; An hypoth- 
sisof the structure of the copper belt of the South Mountain, pp. 82-85. Henderson, The copper 
eposits ot the South Mountain: Trans. Am. Inst. Min., Eng., Vol XII, pp. 85-90. 
