There is some interesting mining history here in the South Central PA area. We don't usually think of mining here, but in the late 1800's there were many. It seems that where the South Mountain pushed up through the earth it deposited various types or iron ores and clays. From Mount Holly around the end of South Mountain to the ironsworks at Boiling Springs, to Dillsburg, and on down into York county there are iron ore deposits.
The ironworks at Boiling Springs dates back to 1762.
In 1847 a Dillsburg farmer named Abraham Mumper discovered rocks which turned out to be a rich black magnetite ore. This led to series of mines opening in the area. Notably, one was at Mumper Lane and Ore Bank Road, at the top of a ridge just east of town. Other mines opened in the Dogwood run area on the west side of town, as well is in the area now known as Camp Tuckahoe. These mines operated until 1908. Thomas Edison visited the mines in 1906.
In Mount Holly there are large deposits of hematite ore which is still mined there east and south of town.
There are several large quarries in the area, including one near White Hill Correctional Institution, one at Locust Point and one off the Carlisle Pike near Wal-Mart.
There are a number of old quarries in the area too. One is located near White Rock Acres, a small one is located at Williams Grove.
Aside from the rock strata that is pushed from the surface near South Mountain the rest of the local Cumberland Valley is basically sitting on limestone which is very porous. The water from the entire valley drains into huge underground aquifers, which sometimes erode away at the surface causing a sinkhole. The underground river swells to the surface at Boiling Springs. The water is a constant 52 degrees and bubbles up from caverns that are estimated to be 2000 feet below the surface.
I wonder just what we are sitting on, something like swiss cheese? It's very surprising to me that we do not hear about the discovery of a cave more often.
