78 
VOLCANIC ROCKS OF SOUTH MOUNTAIN. 
[BULL. 136. 
the crushed porphyrites. It also occurs in crystalline form, and at a 
single locality (south of the Fountaindale turnpike, on the north Hank 
of Haycock Mountain) micaceous hematite occurs in veins. Calcite is 
rare. It is occasionally present in the amygdules or as vein material; 
and in the case of a single specimen, broken from a roadside bowlder, it 
almost completely replaces the substance of the rock. 
The range of minerals, original, secondary, and accessory, found in 
the South Mountain rocks is a very limited one. 
DISCUSSION OF CHEMICAL ANALYSES. 
The analyses tabulated below, with the exception of No. IV, are col- 
lected from analyses scattered through the publications of the Second 
Geological Survey of Pennsylvania. For Analysis IV the writer is 
indebted to the courtesy of Professor Daniells, of Wisconsin University : 
Table of analyses. 
I. 
II. 
III. 
IV. 
V. 
Si0 2 
48.93 
"15.42" 
14. 71 
48. 02 
1.45 
17.84 
11,61 
.98 
41.280 
37. 225 
37. 03 
0.51 
C 24. 13 
) 19.03"" 
4.05 
0.21 
1.44 
8.93 
Trace. 
3.54 
P 2 5 
A1 2 3 
18.480 
9.440 
8.200 
( 44.82 
Fe 2 3 
FeO 
Ti0 2 
CaO 
MgO 
K 2 
18.16 
2.78 
18.25 
7 040 
7.486 
2.208 
3.523 
2.740 
15. 79 
1.14 
Na.,0 
(') 
1.50 
Total 
100. 54 
99. 65 
100. 397 
98. 975 
99.67 
1 Not determined. 
I. "Orthofelsite, containing epidote, llf miles west of Gettysburg." 1 
II. "Epidotic rock, 2-\ miles from Mount Alto furnace." l 
III. " Chloritic schist from Bechtel shaft." - 
IV. Differentiated band at the west end of the tunnel. 3 
V. " Variegated chlorite-schist with chlorite ( ?), one-half mile northeast of Pine 
Grove." l 
The characterization of these rocks by the Second Geological Survey 
is somewhat vague, and in the discussion of the analyses the writer 
is again hampered by the lack of baud specimens of the rock analyzed. 
The percentages are about those of the normal augite-porphyrites 
and melaphyres as given in Koth's tables. They scarcely show as 
much variation as the altered augite plagioclase rocks of his tables. 
Although the analyses show some phosphorous pentoxide, no apatite 
was noted in the microscopic study. The iron percentage is high in all 
of the analyses, though not abnormally so — not higher than the micro- 
scopic study would lead us to expect. 
'Second Geological Survey of Pennsylvania, Vol. CCC, pp. 255-275. Analyses made by the late Dr. 
F. A. Genth. 
2 Frazer: Hypothesis of the structure of tho copper belt of the South Mountain, p. 82 : Trans. Am, 
Inst. Mm. Eng..Vol. XII, pp. 85-90. Analysis made hy C. Hanford Henderson. 
s Analysis made by Prof, W. W. Daniells, of Wisconsin University, 
