There is a town in York County that everyone relates it more to Baltimore than York.

This little haven rests in a valley that you can’t see until you are on Main Street. However, this town is full of heritage, especially when it comes to a special rock known as slate. Slate was used as roofing from 1625 to 1670 in Williamsburg, Va., in Boston as early as 1654, and in Philadelphia in 1699.

Imported slate from North Wales was used in the United States during Colonial days. By 1876, slate was no longer an item imported by the United States, but it became a net exporter to other countries. The United States’ roofing slate reached its peak in the period between 1897 and 1914. In 1899, there were over 200 slate quarries operating in 13 states. Pennsylvania was the largest producer, with operations in Northhampton and Lehigh counties; in what is known as the Peach Bottom district in Lancaster and York counties; and extending into Harford County, Md.

The Jones Quarry is a typical looking slate operation with water-filled pit.

The Peach Bottom Slate District is world-famous.  Although the discovery of the slate resources in Delta is credited to Welshman John J. Roberts in the 1730s, the first commercial slate quarry in the United States was opened in this area in 1785 by William Docher. The quarry was situated on the McCandless property and later owned by the Williamson estate.  About 30 quarries operated in the Peach Bottom District until the industry’s end in the 1940’s.  Slate was used for gravestones, fence posts, window lintels, shingles, sidewalks and roofing granules. The shingles were marketed in “squares,” the amount of slate needed to cover a 10-foot square area. From 3,000 to 3,500 squares of best quality slate and 1,000 tons of second quality slate were obtained yearly from some of the best quarries.

It was in the 1840s as the Welsh came to the United States hearing about these rich slate deposits, that the Deltas area began to gain its reputation.  With their quarrying experience in North Wales, techniques of open-pit quarrying were brought to the area.   In 1850, the Peach Bottom Slate was named as the best building slate in the world at the World Expo in London, England.  The country’s largest estate, the Biltmore Mansion in Asheville, North Carolina has a slate roof from Delta. The slate has been used in federal, state and local government buildings, as well as, many private residences and buildings.

The Peach Bottom Slate was too good of a product. Because of its composition, as well as intense heat and pressure during ancient geologic events, the slate never wore out. In fact, the grayish-black slate never changes color because of weathering. The durability was second to none when compared to other slates being quarried in the United States. I know of at least one building in York that has had a Peach Bottom Slate roof for 200 years and have never had a problem with leakage or breakage.

World-famous slate clock housed at the Old Line Museum standing seven feet two inches tall

The Delta area is one of my favorite places to take geologic education trips.  The built-in heritage, preserved sites and still highly controversial geology provides a foundation for a great day in southeastern York County.  A drive through Delta quietly reveals the heritage. Watch for the slate roofs on the buildings and walk carefully of the slate sidewalks when it rains. A glimpse of a rare slate fence post in the ground can be seen. The old bank building on Main Street has been converted to the Old Line Museum that houses many artifacts and photographs of the slate industry. The museum also houses a one-of-a-kind production known as the Slate Clock. Produced by Humphrey O. Prichard in the early 1900s, this hand-carved clock stands seven feet and two inches high and contains different slates from three locations:  Delta and Bangor, Pennsylvania and Vermont.  The clock is held together by 1,300 screws and contains numerous carved motifs of animals.

The orginal jail built entirely out of slate

While in downtown Delta, check out the original jailhouse on Edgar Avenue. The jail was built entirely of slate. The story goes that the builder of jail was its first prisoner, apparently celebrating too much after the finished construction. He also was the first escapee at the jailhouse.

Rehobath Welsh Church, one of only four active congreations in North America.

Heading east on Main Street and continuing onto Atom Road, the Rehoboth Welsh Church still holds weekly services. This is one of only four active Welsh congregations in North America. In May and October the church hosts a Gymanfa Ganu (Welsh hymn sing). Beyond quarrying, the Welsh knew how to sing, which is evident if you ever attend one of these events.

If you continue east on Atom Road and travel past the intersection with Slateville Road, notice the huge slate wast piles on the right side. This lower-grade slate piles are remains of the Funkhauser Quarry, which lies behind the piles. The quarry cannot be seen from the road, but is nearly 0.75 mile long and has depths of up to 175 feet deep (water-filled). The quarry is on private property and well marked as such. In 1998, Funkhauser Quarry was ranked the second most deadliest quarry in the country by the U.S. Department of Labor Safe Mining Division. Public education and security patrols of the property have nearly eliminated the trespassing and swimming on the property. The Funkhauser Quarry property was the site of the first commercial slate quarry in the country, as well as the last quarrying in the Peach Bottom area.

Funkhauser Quarry is 0.75 miles long. The rocks walls are about 70 feet high above the water.

On Slateville Road is the Slateville Presbyterian Church cemetery. This is a great location to see the hand-carved slate grave markers. If you want to talk about talent, examine these markers with all of the detail. To show the durability of the slate, some of the markers still show the scribe lines marking sure the worker keeps the lines straight. Some of these markers go back137 years to 1863 — 137 years ago.

An example of a hand-carved slate grave marker

Notice the faint scrtibe line above "Er Cof" showing the durability of the slate

If you travel southwest on Ridge Road for a short distance from the church, turn left onto Green Road.  This was known as Main Street in Coulsontown.  Today four Welsh cottages exist here with two of them still inhabited.  The Welsh did not mingle with the Scot-Irish residents, but lived in their own villages around the quarries.  Coulsontown was one of three such communities, but the best preserved today.  These cottages are duplicates of the cottages a person would live in Wales.  The cottages are constructed of country rock (here the Cardiff Conglomerate) and of course, having a slate roof.  Along the top of the house there are four courses of brick.  In Wales, those having brick as part of a house was rare and only seen with those homeowners who had money.  The Welsh that immigrated here wanted to think of themselves as elite important people.

Two Welsh cottages at Coulsontown. These two cottages have been recently purchased by the Old Line Museum and are undergoing restoration back in their 1840's appearance. Notice the slate posts and fence in front yard.

The brick courses at the top of the Welsh cottage showing important status of the house owner.

To complete your mini-tour of the Delta area, drive out Quarry Road on top of Slate Ridge and see how many quarries or slate waste piles you can spot. Along the top of Slate Ridge from the Susquehanna River southwestern into Harford County, Maryland contained all of the quarries. Today, these relics give us only a glimpse of what was once a very important mineral resource that placed Delta on the map.

When thinking of a topic for this blog, one of my friends (a history buff) asked me, “Did geology play a role in the Battle of Gettysburg?”

Wow, what a good subject, although some of the information is removed from York County.  However, Gettysburg is such a draw to many historians in this area, why not include it in one of my psts? I was on the Gettysburg battlefield last Friday doing a teacher’s workshop on geology for school teachers.

When I think of the Civil War, I see a soldier carrying his gear and weapon. Horses were being ridden by officers pulling cannons, supply wagons and ammunition. Roads were already established, developed by horses and wagons traveling from town to town.  All of the primary roads were developed along the easiest route to a destination, meaning they were fairly flat. U.S. Route 30, Pa. Rte 194 and Northern Central Railroad (now the York County Heritage Rail Trail) were used by both the Union and Confederate troops.

We know about the historic burning of the bridge in Wrightsville prior to the famous battle. Yes, it was a brilliant maneuver by the Union to destroy the bridge, not allowing the Confederates closer to Philadelphia. If not for the presence of the Susquehanna River between Wrightsville and Columbia, the bridge would never have been burned. Perhaps the Confederates would have advanced toward Philadelphia without hesitation and the outcome of the Civil War may have been different.

A view of Gettysburg from Culp's Hill. South Mountain is the highlands in the backgorund.

On to Gettysburg! South Mountain, the dominate highlands between Chambersburg and Gettysburg, acted as a shield for the Confederates.  75,000 Confederate troops were traveling north through the Cumberland Valley, hoping to get to Carlisle and Harrisburg for well-needed supplies.  95,000 Union troops were on the east side of South Mountain in the Piedmont with little idea where the Confederates were.  The Confederates, who heard about supplies in Gettysburg, turned eastward. Many of the troops came through what was known as Cashtown Pass, now occupied by U.S. Rte. 30 at Caledonia State Park. With the steep terrain of South Mountain finding a gap in the mountain made access fairly easy.

To take this one step further into the geologic side of the story, why is that gap in South Mountain? It actually is the location of a structure known as the Carbaugh-Marsh Creek fault, where the north side of South Mountain moved about two miles west of the south side of the mountain. With the presence of the fault, rocks were broken and accelerated weathering and erosion, producing a gap. Monterey Gap, south of Cashtown Gap near Blue Ridge Summit was another route for the Confederates to come east, but that terrain presented many elevation changes and twisting and turning of the dirt roads. If it would not have been the Carbaugh-Marsh Creek fault, the Confederates had the choice of using Harpers Ferry, W. Va., to the south or travel around the northern terminus of South Mountain near Dillsburg, York County.

A view of the battlefield looking north from Little Round Top. Notice the rolling terrain.

Gettysburg is located within the Gettysburg-Newark Section of the Piedmont physiographic province. The area is characterized by rolling terrain composed of Mesozoic-aged sedimentary rocks sandstone, shale and an igneous rock known as diabase.  Diabase became the main character in the Battle of Gettysburg. This igneous rock is very dense and very resistant to weathering and erosion. Diabase underlies the higher elevations on the battlefield such as Big Round Top, Little Round Top and Culp’s Hill.  Diabase is also found under Cemetery Ridge on the east side of Pickett’s Charge and under Oak Ridge, Seminary Ridge and Warfield Ridge on the Confederate side of Pickett’s Charge. In the case of Pickett’s Charge, the Confederates marched in 3-4-5 formation off of a diabase ridge, down into a shallow valley and then back up heading toward the Corpse of Trees and the High Water Mark. Although the elevation change is only about 40 feet, the movement of weapons, ammunition and supplies was hard for the Confederates.

View of Pickett's Charge looking west from the High Water Mark.

Because a military map of Gettysburg had been prepared prior to any thought of a conflict in the area, Union officers believed that whoever held the position on Little Round Top would probably win the Battle of Gettysburg and maybe the Civil War.  Also, a problem encountered by particularly the Confederate troops was that of the lack of trenching for protection.  A common military practice was to trench to get out of the way of cannon fire and sharp-shooters.  An area underlain by diabase produces either a thin soil or no soil at all.  It was a welcome sight for the Confederates to use the large boulders at Devil’s Den.  That is also why there are many stone walls that were built to provide protection from Union gunfire.

The original Devil's Den. The two sets of white marks are on the left side.

Although many of you have visited Devil’s Den, one of the most popular Civil War sites, there are several things I would like to point out to you. First of all, Devil’s Den is the best example of diabase. The rounded boulders that once formed by magma at least one mile beneath the Earth’s surface about 201 million years ago show the wear and tear of both mother nature and the man-induced damage during the battle.  Look for cracks running against many of the surfaces. These are cooling cracks as the magma cooled at varying rates, forming cracks. These cracks are similar to a mud puddle drying up after a rain, cracking the dirt.  The rounded shape is known as spheroidal weathering, a characteristic of igneous rocks and particularly diabase.

A view of Little Round Top from Devil's Den

On the lower side of Devil’s Den at the southwest corner near the parking lot, how many of you have noticed a large diabase boulder containing concentric rings running across the vertical face? If you look near the upper right side of the large boulder, you may see a flatten edge that looks out of place. Resembling a large-scale example of a prehistoric person striking a rock to produce a stone tool, this diabase boulder is evidence that a cannon ball struck the rock at the flatten area. The concentric rings reflect the percussion waves that traveled through the diabase

I take a break on a diabase boulder. Notice the cooling cracks behind me?

At the east side of Devil’s Den, where the steps go up through the boulders, you will see a rock lying on two large diabase boulders, creating a “cave.”  This is the original Devil’s Den.  If you go into the “cave” and look where the overlying rock meets the bottom rock, you will see two sets of white lines.  These paint lines were placed there by geologists many years ago to track any movement of these unattached diabase boulders.

So, yes, the geology played a role in the Battle of Gettysburg.  If it was from the lay of the land that involved planning for attacks, to providing protection for the troops to finding fresh water at springs, you cannot study this history without considering the geology.

As I write this post, the weather outside is damp — not a good time to get the yard ready for its long winter nap.  So, feeling a little depressed, I chose to write about depressions in the Earth, known as sinkholes and associated caves.

York County has its share of limestone and dolomite (known as carbonate rocks due to their chemical makeup).  Limestone is a sedimentary rock composed of at least 50% calcium carbonate (a mineral known as calcite).  Dolomite is a sedimentary rock composed of less than 50% calcite, but at least half of the rock is made up of the mineral dolomite (magnesium carbonate).  Sinkholes and caves often form in carbonate areas.  Both limestone and dolomite formed on an ancient continental shelf in a tropical sea in this area between 550 and 460 million years ago.

The south wall of the York Building Products - Roosevelt Plant quarry showing bedding in limestone.

So where are the carbonate rocks in York County?  The area known locally as the York Valley is underlain with these rocks.  Known to geologists as the Lowlands Section of the Piedmont physiographic province, U. S. Route 30 maps the limestone and dolomite for us.  From the Susquehanna River westward to Farmers in western York County, limestone and dolomite are commonly seen in the small roadcuts.  From the intersection with U.S. Route 30 at the 5-Mile House near Thomasville, Pa., Route 116 to Hanover follows a carbonate valley.  Wrightsville, York and Hanover all have these sedimentary rocks underlying them.  A third section of carbonate rocks runs from Emigsville northeast to the Susquehanna River at Saginaw.   After all, the areas containing limestone and dolomite have been or are being quarried for the rock, but that is for another time.

Crossing the center of the county is the famous carbonate belt containing good quality limestone and dolomite.

Sinkholes and caves are interesting to observe and explore when done with an expert.

However, the development of a sinkhole or collapse of a cave can cause damage on the surface or to a man-made structure.  Both caves and sinkholes belong to a group of natural features known as geologic hazards.  A sinkhole is a depression in the Earth’s surface caused by the failure of the bedrock.  It may be caused by acid rain or groundwater slowly eroding the carbonate rock, especially limestone.  Cracks in the limestone will continue to expand through erosion, and the crack eventually becomes a large void.  Gravity pushes down on the void, creating a funnel-shaped depression in the surface.  Another way for a sinkhole to form is by the collapse of a cave roof.  When the roof of a cave falls in, all of the material above it cannot hold its weight, causing a sinkhole.

A sinkhole in the field on the north side of Oxford Road in Oxford Township, Adams County

Some of you may know of specific examples where sinkholes and caves have created trouble in York County.  As a youngster, I enjoyed exploring a part of the York Valley in my neighborhood.  Not realizing the dangers of sinkholes and caves, friends and I would crawl in and out of openings and short cave passages on Saturdays.  Today, that area is the site of the West Manchester Mall and U. S. Route 30.  The numerous sinkholes and caves there reminded me out an enlarged groundhog den system.  In the last 20 years, Route 30 had lane closures because of active sinkholes as well as repeated landscaping in the field between the mall and the first interstate highway in the United States.

A clay-filled sinkhole encountered at the Codorus Stone Supply Company quarry in East Manchester Township

Another example of a cave system affecting construction occurred at the parking garage at the corner of West Philadelphia Street and North George Street.  It was reported that the garage design had to be modified after the start of construction after a cave was found under the foundation.  The most recent example of sinkhole damage in the York area occurred in March 2010, when two houses on West Philadelphia Street had to be destroyed after a large sinkhole opened beneath one of them.

Just outside of York County, traveling on Oxford Road in Oxford Township north of Hanover, you may have spotted a unique highway sign: “Travel at Your Own Risk – Sinkholes.”

A number of caves have been explored and mapped in York County.  It seems that many of the larger caves have formed on the border between a softer limestone against a more durable limestone or dolomite.  Groundwater running through the softer limestone etches the rock away while the more durable rock stands its ground.  Names like the West York Cave (West Manchester Township), North York Cave (Manchester Township), Emig Cave (Manchester Township), Willis Run Cave (West Manchester Township) and East York Cave (York Township) come to mind of caves that have been documented.  As a reminder, caves are on private property and are dangerous places.  Exploring caves should be done with an expert.  Many cave entrances are destroyed to eliminate access to them.

On February 24, 1980, a visitor to the then un-developed John Rudy County Park in East Manchester Township made headlines. The lower elevations of the park are underlain with limestone and dolomite; the ridge at the northern edge of the park is made up of a harder, durable rock known as quartzite. While the visitor was riding his horse up the hill close to the present-day BMX track, one of the horse’s legs suddenly fell into what appeared to be a groundhog hole.  When the belly of the horse hit the ground, the surface collapsed into a sinkhole that measured about 8 feet deep and 10 feet in diameter.  Luckily, no one involved suffered any injuries, and it took a parks maintenance worker with a bulldozer about one hour to lower a ramp into the sinkhole to retrieve the unharmed horse.

On inspection of the sinkhole, all of the rock in the soil was quartzite and not carbonate rock. The sinkhole occurred a short distance uphill from where the carbonate rock is found. I suspect that a subsurface sinkhole had occurred some time before in the carbonate rock with a bridge of quartzite over the void.  When the weight of the horse pushed the ground down, everything above the subsurface sinkhole fell.  An unusual but interesting event.

Thanks to the alertness of a train engineer, a diaster was avoided near Thomasville. The sinkhole appeared in 2009 and has been repaired.

Another sinkhole known as the Bootlegger’s Sink in Manchester Township is world-famous for its contents. Fortunately, with development surrounding the feature, those involved saw the importance of preserving Bootlegger’s for future generations to research.  This sinkhole will be a subject of a future post.