bascom.] HISTORICAL REVIEW. 17 
localities reduced, almost to the state of kaolin. Nothing which might correspond 
to the term sandstone was ohserved, though all the above sediments were free of 
grit and sandy particles. * * * It seems fair to conclude that the region of the 
copper-bearing rocks belongs to the Huronian cycle. 
With these views Dr. T. Sterry Hunt expressed entire concurrence. 1 
Dr. Hunt had previously made some study of the South Mountain 
rocks, and published, at various times, his observations concerning 
them. In 1876 he said: 2 
In the southern part of Pennsylvania, to the west of Gettysburg, this moun- 
tainous belt, rising between the Mesozoic on the east and the great limestone valley 
on the west, presents an immense development of a peculiar type of crystalline 
rocks which I detected there last year, and which has a considerable geological 
importance. It is a bedded petrosilex, grayish, reddish, or purplish in color, some- 
times granular but more often jasper-like in texture, and frequently porphyritic from 
the presence of small crystals of orthoclase-feldspar or of glassy quartz. There is 
found here a great breadth of this rock distinctly bedded, presenting different varie- 
ties, and alternating with dioritic, or diabasic, epidotic, and chloritic rocks, with 
argillites, in which are sometimes included thin beds of the petrosilex, the strata 
generally dipping at high angles to the east. 
These rocks Dr. Hunt provisionally referred to a position near the 
base of the Huronian division, adding: 
This petrosilex is identical in its lithological character with the hiilleilinta, or 
stratified flint rock of the Swedish geologists, which is by them assigned a similar 
position, i. e., above the most ancient gneisses. 
In 1878 Dr. Hunt expressed essentially the same views, 3 and in 1879 4 
he opposed the correlation of the South Mountain rocks with the copper- 
bearing rocks of Lake Superior (Keweenawan series), although at an 
earlier date he notes a resemblance. He says : 5 
I may also note that I have observed bedded petrosilex rocks like those just 
noticed [South Mountain porphyries] to the north of Lake Superior, both in an 
island south of St. Ignace and on the adjacent mainland. The conglomerates or 
breccias, which, in the rocks of the Keweenawan series on the south shore of the 
lake, include the native copper of the Calumet and Hecla and the Boston and Albany 
mines, are also made up of the ruins of a precisely similar petrosilex porphyry. 
In October, 1879, Mr. J. F. Blandy made a brief reconnoissance of 
the lower portion of the South Mountain with not unfruitful results. 
He makes a suggestive correlation of the copper-bearing rocks of 
southern Pennsylvania with the Lake Superior copper formation, 6 
thus recognizing the volcanic nature of the greenstones, at least, 
which he called "amygdaloidal trap." The acid rocks still remain 
"slates." 
In the final report of the Pennsylvania survey, 7 Professor Lesley 
' Trans. Am. Inst. Min. Eng., Vol. VII, 1879, p. 339. 
2 Proc. Am. Ass. Adv. Sci., 1876, pp. 211-212. 
i Second Geol. Surv. Pa., Vol. E, p. 193. 
4 Trans. Am. Inst. Min. Eng., Vol. VII, p. 331. 
5 Proc. Am. Ass. Adv. Sci., 1876, p. 211. 
« Trans Am. Inst. Min. Eng., Vol. VII, pp. 331-333. 
7 Final Peport of the Pa. Geol. Surv., Lesley, Summary. Vol. 1, 189?, 
Pull, 136 ^ 
