Sunday, March 16, 2014

Cornwall Ore Banks and Iron Furnace

Who would have believed, traveling the through the Appalachia foothills of Pennsylvania, that such an unobtrusive hill would contain such natural and mineral wealth?  Yet, nothing less than the greatest ore deposit ever found in the New World lies beneath this ridge. Not until a larger deposit was discovered near Lake Superior did a young nation have such a reliable ore resource as the Cornwall Banks. And who would have believed that this deposit would keep on giving for two centuries? On this Charter Day, March 9, 2014, I decided to spend the day celebrating William Penn's founding of Pennsylvania, March 9, 1681, by visiting the Cornwall Iron Furnace.

Hand carts for delivering loads of charcoal to the furnace.
How does an old iron furnace figure into a blog about natural history? Natural assets figured pretty well by the standards of a young nation that had to defend, feed, and heat itself, as well as build an economy that would sustain it. Natural resources of a new nation, discovered and utilized by men of means and ideas, defined the colonial drive for independence. Unlike today, where we are detached and disconnected from the day-to-day connection to minerals, forests, and stone. By comparison, colonial and post-colonial citizens of the Commonwealth knew a thing or two about nature, like how a glob of iron ore dug out of the ground would become a cast iron frying pan, a cannon, or hinge straps for the Meeting House door.

This enormous flywheel, 76 feet around, powered originally by water, then later by a steam engine, worked the bellows that forced air through pipes into the four sides of the furnace stack to heat the flux, fuel, and ore.
The Cornwall Banks provided everything needed to construct and operate for two hundred consecutive years a world class iron furnace with its foundries and forges. The valley provided clay for bricks, sand for mortar, limestone and sandstone for foundations, walls and the furnace stack itself. The wooded ridges provided timber for flywheels, handcarts, tool handles, buckets, troughs, rafters, floors, firewood, and charcoal to fire the furnace. Stone and wood built the miner's villages in and around the main open pit mines at Cornwall, as well as the elegant homes of the the iron masters and owners.

Furnace lift gate drew liquid iron into the channels. All who worked in this room were highly skilled. The stack is a fine construction of beautiful red sandstone, 28' square at its base.

The human history of the Cornwall Iron Furnace is well explained in its museum and website. This post however, is about the natural resources that made a large industrial site possible and what happened when the industry collapsed. The short of it is that nature giveth and nature taketh away!

Triassic sandstone and valley limestone line the street in the walls of these miners cottages.
The ridge and the valley that make up the Cornwall Iron Furnace region tell of the long, rich geologic history of Pennsylvania. The Cornwall  ridge, a section of the Iron Hills, is a 500 million year old remnant of the Appalachian mountain building event, a great thrust-faulting and folding of the surface from (what is now) Georgia to New Jersey. An oceanic plate, forced under the eastern continental edge by the powerful drifting of the North African plate, created such friction that deep bedrock was liquified and uplifted; a very active volcanic period for these parts! Almost as soon as they rose, the Appalacians began to erode, leaving thousands of feet of sedimentary deposits. Interior seas opened and closed. Marine and freshwater deposits were laid down. And, as North Africa drifted away and the Proto-Atlantic opened, cracks formed along the shoulders of the continent, the result of stretching crustal zones. These were quickly infused by more molten material. The contact zone between the older sediments and the new igneous matter, over time, created a wealth of new minerals and ores that in the Cornwall Hills that was very accessible to people. And very deep.

What is now Cornwall Lake is the flooded open pit mine of the Cornwall Banks, 400 feet deep!
The magnetite ore banks, the result of contact metamorphism between the intrusion of Triassic diabase into the stretched and broken Cambrian limestone hundreds of millions of years ago, lay close to the surface at the time it was discovered in 1739.  Two hundred years of mining deep down into ridge, laid open a huge pit mine and around this enormous operation, thousands of people worked and lived in what became a thriving and heavily industrial landscape. Factories, machine shops, a railroad, shanty towns, stables and engine houses, stone breakers, miles of roads and tracks flanked the mines. This is a great composite video of the Cornwall Banks from the 1850s until it closed:

By the time nature put an end to the enterprise, 40 million tons of ore had been removed from the mines. The mines closed seemingly overnight when Tropical Storm Agnes blew inland in 1972. Catastrophic flooding occurred throughout the Mid-Atlantic, and hit central Pennsylvania especially hard. For Cornwall mines, high on the ridge, the floodwaters came from below, surging up through the shafts and underground springs so rapidly that the huge pumps that normally dealt with rainfall and snowmelt at the bottom of the pit, were overtaken and rendered useless within hours. The furnace, forges, and foundries closed the following year, unable to recover.

What remains of the Cornwall iron industry is a historical footnote  to the immensity of the operations here, and reveals little of the power of nature to bring to a close two hundred years of productive ore mining.

Though the landscape looks far different than it did just a hundred years ago, the historic furnace and surrounding main streets are well preserved. The main furnace compound is now a property of the Pennsylvania Historical and Museum Commission that maintains an excellent small museum and walking tour of the grounds and buildings. What I find more interesting is how quickly and thoroughly nature has reclaimed this once booming industrial center. I walked several miles of trails in the nearby Game Lands and plan to return to bike the 14 mile rails-to-trail path that connects this area to Mt. Gretna, the Victorian summer resort town that hosted many iron industry workers and their families for vacation.

The landscape was transformed many times over. Continental collisions, mountain building, erosion, ore banks, industry, and a catastrophic weather event that ended an era of human history. As a rock hound, environmental historian, and naturalist, this is a five star area to explore. I'll put up a another post that focuses on the Lebanon Rail Trail and Mt. Gretna, but it was the Cornwall story that leads to many others!


Cornwall Iron Furnace

Pennsylvania Historical and Museum Commission

Cornwall Iron Furnace Film (seen in the visitor's center as well as on You Tube):

A map of the Lebanon Rail Trail:

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