in Pennsylvania and Maryland. 485 



bedded with hydrorrhea and chloritic schists.* Regarding the 

 origin of these latter rocks, which like the conglomerate were 

 placed below Rogers' primal sandstone, Dr. Frazer made the 

 following statement in 1877, f repeating it two years later \\ 

 " The porphyry which carries the copper of this region shows 

 no character of igneous action, but occurs in coarse and thin 

 beds, more or less disintegrated, and in some localities reduced 

 almost to the state of kaolin." 



Dr. T. Sterry Hunt announced to the American Association 

 for the Advancement of Science in 1876 that he had identi- 

 fied petrosilex or hallefrinta in South Mountain, which he had 

 examined with Dr. Frazer.§ Dr. Hunt's concurrence in 1879 

 with Dr. Frazer's opinion above cited, and his constant use of 

 the term bedded petrosilex sufficiently indicate that he re- 

 garded these rocks as sedimentary. He however correctly 

 compares the South Mountain rocks with others in Missouri, 

 the Lake Superior region, eastern Massachusetts, Maine, and 

 New Brunswick, since shown to be volcanic, although he saw 

 in this similarity only evidence of their " Huronian " age. 



The nearest approach to a recognition of the South Mountain 

 rocks in Pennsylvania as volcanic was made by Mr. J. F. 

 Blandy, who described the copper-bearing rock in 1879 as 

 amygdaloid trap, and correlated it with the similar flows near 

 Lake Superior. The acid felsites however were regarded by 

 Mr. Blandy as slate. || 



In his recent final volume on the Geology of Pennsylvania, 

 Professor Lesley follows in the main Dr. Frazer's classification 

 of the rocks of South Mountain. Although he considers that 

 the sandstone probably represents the " Huronian " of Logan 

 and Murry, he says it is impossible not to compare it with 

 Walcott's Cambrian System. The supposed overlying feld- 

 spathic felsite series (orthofelsite of Frazer) Lesley estimates 

 as 6,000 feet in thickness, and everywhere speaks as though he 

 regarded it of sedimentary origin.^" 



The cause of the prevailing misconception regarding the 

 volcanic rocks of South Mountain is not difficult to find. 

 Their accompanying accumulations of tuff beds and breccias, 

 and the fact that they are generally cleaved parallel to the 



* Report of Progress in the counties of York, Adams, Cumberland and Frank- 

 lin. Second Geol. Surv. of Penn. CC for 1875. Harrisburg, 1877, p. 285. 



+ "Copper Ores of Pennsylvania." Polytechnic. Review, vol. hi, p. 170, April 

 28,' 1877. 



% Trans. Am. Inst. Min. Engineers, vol. vii, p. 338, 1879. 



§ Proc. Am. Assoc. Adv. Sci., 1876. pp. 211, 212, and Second Geol. Survey of 

 Penn., vol. E. 1878, p. 193. 



|| " The Lake Superior Copper Rocks in Pennsylvania." Trans. Am. Inst. Min. 

 Engineers, vol. vii, p. 331, 1879. 



if A Summary description of the Geology of Pennsylvania by J. P. Lesley, 

 State Geologist, vol. i, p. 146, 1892. 



