Jan. 3, 1873.] & [Lesley. 



THE IRON ORES OF THE SOUTH MOUNTAIN 



Along the line of the Harrisburg and Potomac Railway, in 

 Cumberland County, Pennsylvania. 



(Read before the American Philosophical Society, January 3, 1873.) 

 By J. P. Lesley, 



Professor of Geology in the Department of Science, University of Pennsylvania. 



The Harrisburg and Potomac Railroad, starting from Harrisburg and 

 running along the North base of the South Mountain, has for its objective 

 point Shepherdstown on the Potomac, but its Western terminus has 

 not yet been absolutely determined. It follows the Yellow Breeches 

 Creek along the North foot of the South Mountain in Cumberland 

 County, Pennsylvania. It runs parallel to Cumberland Valley Railroad, 

 and distant from it, on an average, from four to six miles. 



The Cumberland Valley is divisible into two parts, or belts, the one 

 being slate land, the other limestone land . The Cumberland Valley Rail- 

 road may be taken as the line of demarcation between these two belts 

 of Lower Silurian outcrops, running as it does nearly along the northern 

 and northwestern edge of the limestone land. The interval, therefore 

 between the two railroads is all limestone land. 



This limestone belt is full of nests, pockets and strips of brown hema- 

 tite ore, some of them small, others large . They have been opened by 

 the fanners in, at least, sixty places between Mechanicsburg and Clevers- 

 burg, a distance of thirty miles. Fifty-seven of these ore-diggings are 

 marked upon the map which accompanies this paper. But the number 

 of ore deposits is indefinitely great. Probably several hundred mines, 

 great and small, might be opened. Those actually opened are mostly 

 mere trial pits from which a few hundreds or thousands of tons of ore 

 have been dug, at the convenience of the farmers, and sold to the small 

 charcoal furnaces built at different times during the last half century. 

 No scientific exploration has ever been undertaken to test their real size, 

 width, length and depth ; nor has any geological tracing of the deposits 

 into each other been made. The whole may considered unexplored 

 ground. No geologist can doubt for a moment that large quantities of 

 wash ore, clay ore, rock ore and pipe ore lie concealed under the surface 

 soil of the fields. 



Passing to the south side of the Harrisburg and Potomac Railroad the 

 geologist finds himself on a belt of country of a different kind, full of 

 deposits of brown hematite iron ore, belonging to another and older 

 series. To make this clear, I must give an ideal cross-section of the 

 valley and the mountains which bounds it on the north and on the south. 

 See Fig. 1. 



