Stop 1. Specialty Granules Corporation, Charmain Road, Blue Ridge Summit, Blue Ridge Summit, PA Geologic Formation: Catoctin of Precambrian age Rock type(s): Metabasalt (greenish) and metarhyolite (reddish) (volcanic) We are grateful and excited about presenting this stop to you. Thank you goes out to Greg Oliver and Charlie Poulson of Specialty Granules for all of the pre-fieldtrip planning and our tour today. They have volunteered to come to the operation to host our tour and their assistance is greatly appreciated. It is hoped that you will see how valuable quarries are, appreciate how technology is used in producing their finished products and realize how many regulations such an operation as Specialty Granules has to follow from the local to federal levels of government. Below are highlights of this operation: Acreage Owned: Over 700 acres Duration: Have been here for 90 years Crushing and screening: Metabasalt is screened from 1.5” to granules Products Producing: Roofing granules in 16 different colors for mostly GAF, Tamaco and Elk Process: Granules are colored and fired. Also produced are unfired, uncolored granules that do not specs. Amount: 600,000 tons shipped of metabasalt granules Transportation: 80% of products are moved by trucks; 20% by railroad Employees: 140 with an average length of service of 17 years Quarry Depth: Current quarry is permitted to 8 levels (approximately 400 feet) Old quarry was down 7 levels (350 feet) but has been back-filled about 250 feet Conveyors: Have 0.75 miles of conveyors to transport rock to different plants and processes Undersized: Have about 50% of the material (600,000-700,000 tons) which is recycled and reclaimed back into quarry Blasting: Once every 7 – 10 days. Have 2 portable seismographs that are deployed out to closest Residences to monitor ground shaking. Problems: The operation often encounters the metarhyolite which no use for is known as this time. Groundwater: No issues since the bedrock is non-permeable and had no porosity Property Border: A beam surrounds the entire border, plainly marking a “Do Not Enter” area. Wildlife: Actual the property can be viewed as a wildlife refuge. Whitetail deer, turkey, bear, coyote, fox, raccoons and birds love this habitat. Other: Have a pond to settle out sediment before entering back into the watershed. Water re-entering watershed is probably cleaner than stream water. Have a on-site weather station to monitor conditions, i.e. for blasting. Geology: Metabasalt and metarhyolite are both igneous rocks that originated from lava. The word” meta” has been placed in front of each rock name because the rocks have undergone metamorphism through crustal plate collisions. Rhyolite forms from volcanic activity on continental crust and basalt is the major component of oceanic crust. These rocks originated as a result of the breakup of an ancient supercontinent known as Rodinia that split apart starting about 700 million years ago. Later, a collision with a chain of volcanic islands and the coming together of Africa and North America caused heat and pressure, slightly altering the rocks. On the tour, we will try to show an example of folding and faulting in the rock.

Specialty Granules quarry

Point of Interest A Native Copper Mines in South Mountain Location: From near Mt. Hope southward to Pa. Rte. 16, mostly associated with Copper Run. Once belonging to the P. H. Glatfelter Company of Spring Grove, PA as one of their tree farms, many of the mines are today situated within the Michaux State Forest. Several mines were known on the property of Specialty Granules as well as near the “Underground Pentagon.” The first copper operation was reportedly opened in 1833 and became one of the country’s leading copper districts in the late 1800’s. The last major mining operations shutdown in the 1920’s. Occasional attempts and rumors to start new mining continued into the 1960’s. The area became known to “rockhounders” after several reports were published by geologists in the early 1900’s. The district was also publicized in the “Mineral Collecting of Pennsylvania” published in 1976 by the Pennsylvania Geological Survey. An assortment of minerals, including native copper, have been found on the mine dumps. It was reported that native copper was found during the construction of the “Underground Pentagon.” Specialty Granules also finds native copper during quarrying. Native copper is common within volcanic rocks. The Keweenawan copper deposits in Michigan is geologically similar to South Mountain. Most of the copper is found within the metabasalt and quartz veins associated with this rock. The green color of the metabasalt is not from the copper, but rather epidote and chlorite. The copper was formed from deep groundwater containing the native element, which leached toward the surface rocks undergoing hydration. Weathering of the surface rock created secondary minerals such as malachite, azurite and cuprite. The quartz veins were formed in similar fashion where silica and copper ions crystallized from hot groundwater caused by metamorphism. The groundwater found it’s way into cracks within the metabasalt, cooled and formed the copper-bearing veins. For a detailed description on the history of this copper district, go to http://www.pennminerals.com/Chronicles2.htm.

Jeri and Roxann at the Reed Hill copper mine near Mt. Hope

Point of Interest B Devil’s Race Course, Fort Richtie Road, Franklin County Location: Parking area is located on the west side of Ritchie Road about 0.75 mile north of the intersection of Md. Rte. 491 (Raven Rock Road). Although there is a similar occurrence with the same name just northwest of Specialty Granules, we are going to drive past this Maryland occurrence. Although time does not permit us to stop, please come back and visit this geologic feature. The Devil’s Race Course is known as a boulder field composed of boulders of the Weverton quartzite. The feature is approximately 0.70 mile long and 80-130 feet wide. The boulder field was formed by intense weathering and erosion during the “Ice Age.” These boulders were once part of large outcrops of the Cambrian-age quartzite (metamorphosed sandstone) which got broken into boulders and brought down the valley. A stream can still be heard running under the boulders.

Stop 2. Panning for Gold East Branch of Antietam Creek (need permission) Washington County Solid Waste and Recycling, Bikle Road in Smithsburg, MD. The art of panning for gold has intrigued humans for many years. Since the discovery of gold near Charlotte, NC in 1803 which led to the first commercial gold mine in the United States to the gold rush at Sutter’s Mill, CA, people always get excited when they hear “gold.” Although the author has never panned for gold in this vicinity, you can still learn the how’s and why’s in this short stop. The East Branch of the Antietam Creek flow off of the west side of South Mountain and actually originates within the Catoctin Formation metabasalt. Gold, like copper, forms within volcanic rocks. However, with my experience as well as other recreational panners, gold within South Mountain in Pennsylvania appears to be almost non-existent. It appears that gold within the Catoctin Formation is not very common. The area of our panning is underlain by the Cambrian Tomstown Formation, composed entirely of limestone. You will be instructed here on how to fill your gold pan with sediment and using the water, have the heavy minerals settle to the bottom of the pan and the other “junk” rock washed out of the pan. Heavy minerals would include magnetite (black sand), garnet and possibly gold. We will supply you with a small container if you would like to take your “heavy” minerals home for a souvenir or closer look. History of Gold in Maryland: The following is taken from “Gold in Maryland written by Karen Kuff (1987) published by the Maryland Geologic Survey. Maps and more information can be obtained at http://www.mgs.md.gov/esic/brochures/gold.html “Although gold was first reported in 1849 on Samuel Ellicott’s farm near Brookville, Montgomery County, no production was recorded. There are numerous versions of the first discovery of gold in the Potomac area. In 1861 during the Civil War, a Private McCleary (or McCarey) of the 71st Pennsylvania Regiment (or “1st California Volunteers”) was stationed outside of Washington, D.C. While encamped in the vicinity of Great Falls, he discovered gold. It is reported that the gold was found while washing skillets in a stream near McCleary’s hilltop camp overlooking the old Anglers Club. By 1867 the first shaft was sunk near the site of the Maryland Mine.” “Gold has been mined, panned or prospected intermittently since that date. Active mining ended prior to World War II in 1940 and the last recorded production from prospecting was 21 ounces found between 1950-51. The accompanying graph shows gold production in Maryland from 1868 to 1940. Prospecting continues even today. There is a surge of gold panning interest every few years, especially following an increase in the price of gold.“ “No great fortunes were made by Maryland gold miners. In 1890, Emmons stated that there was little likelihood of any new ventures that would result in sure riches for the operator.“ “On all of this belt …there is no record of any great mine the product of which can compare with the few enormously productive mines…in the west, and there seems to have been a very large proportion of disastrous failures among the many gold mining enterprises that have been undertaken here. There is some reason to assume that many of these failures have been due to ignorance and bad methods of working…the depth to which the rocks have been rotted and decomposed…has tended to make the surface showing underly rich; and has been an important factor in preventing systematic and successful mining in depth.” “Not all gold was obtained as ore from mine shafts; much was found by prospecting with trenches, or panning in local streams. The area around Great Falls has yielded most of the gold found in Maryland. Individuals hoping to find gold in Maryland are still looking in this area. Gold recovered by panning is mostly very fine grained but can range up to coarse sand size. Rarely, nuggets were found, some weighing as much as 4 ounces.”

Gold on top and magnetite on bottom of pan

Stop 3 George Washington State Park, Alt. Rte. 40 Boonesboro, MD Monument (Milk Bottle) composed of Weverton Quartzite If you have or never visited this first monument constructed in honor of our first President of the United States, it is always worth a visit. Each time you walk the short trail up to the monument you see something different. Closely examine the quartzite that composes the monument and enjoy the scenic view from the top of South Mountain. New landmarks are seen every time. Quartzite is a metamorphic rock, once a sandstone that has undergone heat and pressure associated with crustal collisions. The rock did not change chemically, but only texturally. Quartz is still the dominate mineral in the rock. Quartzite is coarser-grained due to the grains welding themselves together to make a larger quartz grain. The rock is hard (7.0 on the Moh’s Hardness Scale). Walking up the trail, float of quartzite are lying all over the ground. Examining the rock in the monument you can trace some indication of bedding. No fossils are present. Also, use your keen eye to pick up several quartzite blocks that appear to have 2 directions of bedding (layering) in the rock. This is known as cross-bedding which represents two directions of wave action at a beach when the rock was beginning to form as sandstone. The Weverton quartzite was used in many of the area’s historical buildings. Because of its durability and blocky shape, it is considered a long-lasting stone for buildings. Although rather hard to cut, the rock would be pretty polished after being cut. Ever wonder where the rock came from when you view a historic building? Chances are that the rock originated close by and hard by horse and wagon. For example, in the case of the Washington Monument, the rock came from right here. As we exit the park and return to Alt. Rte. 40, check out the church on the left side just before we travel down off of South Mountain. From the overlook, you are able to see at least 38 miles. Sidling Hill located on Interstate 68 west of Hancock appears as a notch in the mountain to the west. This section is known as the Valley and Ridge Providence or also called the Appalachian Mountains. This famous mountain range is composed of sedimentary rocks such as limestone, sandstone and shale ranging in age from Ordovician to Pennsylvanian. The wide valley below us is the Great Valley Section of the Valley and Ridge. The reason it is a valley is because the rock is mostly limestone and dolomite with some shale beds. Limestone and dolomite are rather soft, not holding up to the elements of weathering and erosion well, thus underlying valleys. Check out the framed photographs of the scenery on top of the tower which has landmarks indicated.

View looking west from Washington State Park

Point of Interest C Middletown Gneiss Exposure on MD Rte. 17 east of the Catoctin Creek, south of Middletown, MD With time restraints we are not able to show you this roadcut, but we have supplied enough samples for everyone to take home probably the oldest sample you have collected. This rock is known as gneiss, a metamorphic rock that illustrates to geologists just how intense the heat and pressure can become during a metamorphism event. This rock underlies much of the Middletown Valley, but exposures are rather obscure. The gneiss was originally a piece of a granitic crust making up a part of an ancient supercontinent known as Rodinia. The rock has been dated at about 1 billion years old. The rock was later involved in the pulling apart of Rodinia, the collision of a volcanic island arc to the east and the great African-North American collision to form Pangaea. Only if the rock could talk, what a story it could tell!! Gneiss is the highest grade metamorphic rock known. If the rock would have had more heat and/or pressure added, the material may have returned back into magma. When the rock was undergoing metamorphism, the white-colored minerals grouped themselves in a zone and the dark colored minerals gathered into their own zone, giving the gneiss a banded appearance. This rock is also believed to be the oldest rock found deep within South mountain and Catoctin Mountain in Maryland. Enjoy your gneiss!!

Point of Interest D Limonite (Goethite) from an area iron mine Again, because of time restraints, we will supply you with a sample of limonite, a.k.a. goethite. This ore was removed from a number of 19th century iron mines in this region and used in nearby furnaces to manufacture iron. We will see one of those furnaces at our last stop. Most of the mines were open pit, not requiring deep shafts to extract the ore. Much of the ore was laying loose in the clay which only required it to be washed and not removed from bedrock. Pick and shovel were about the only required tools. Horse and wagon removed the ore to its processing station or transported it to the furnace. Where blasting was required to dig into the bedrock, dynamite was not used commercially until 1890. Black powder was the main way to loosen the rock prior to 1980. Be careful, your hands will get dirty handling the limonite.

Stop 4 “Potomac Marble” exposure on Ballenger Creek Pike near the Substation 1.17 north of Points of Rock Road Rock Type: Breccia (Sedimentary) but known as a Fanglomerate due to its origin Age: Triassic Period With my experience of regional geology in southeastern Pennsylvania and now into Frederick County, Maryland, This is the nicest exposure of this rock that I know of. I read about this exposure in a book on Frederick County and Richard Gottfreid, professor geology at Frederick Community College suggested this stop. I have seen the fanglomerate quarried, sawed and polished from a farm in Lancaster County, Pennsylvania and wow, is it ever a pretty rock? Imagine that, seeing the large limestone angular boulders set in a reddish clay matrix, glued together. Yes, the rock has been used in several locations as an ornamental stone. The most famous is for pillars inside the National Capitol in Washington, D.C. I am sure there are smaller uses for the rock such as coffee table tops, chair molding in a room or around a fireplace. Just how did this rock form? The rock is considered Triassic in age. During this time, the area was located at about the same latitude as Miami, FL. The climate was tropical with abundant rainfall. It was also the time that the supercontinent Pangaea was beginning to split apart into the world as we know it. We are standing in what was a rift valley, similar to today’s example of the Red Sea. Land to our west was trying to go with North America and the crust to the east was going with Africa. The land here was sinking during the rifting and the valley walls were very steep. As streams flowed from the east into the rift valley, the streams had plenty of velocity coming down the valley slope and were able to carry larger rock fragments. Once the stream flowed out onto the valley floor, the stream’s velocity dramatically slowed and was forced to drop all of the boulders of limestone. As boulders were deposited on top of older boulder layers, as viewed from the air, the sediment appeared as a fan shape, thus known as an alluvial fan. In a dictionary, the rock would be classified as a breccia (rock containing angular fragments). Since we know the specific origin of the rock as an alluvial fan, the rock is known as a fanglomerate. Notice how the limestone is slightly more resistant to weathering and erosion than the reddish clay. The boulders are a little higher off of the surface. Let’s see who can find the largest limestone boulder!! It is hard to determine any bedding in the rock since the deposition was massive. The fanglomerate is estimated to be about 200 feet thick and exposures are localized. You will see the rock lying on the surface more often than in actual outcrops. Another factor is that these alluvial fans were not continuous along the end of a rift basin, but were spotty. It was reported by the Fredrick County School District website dealing with a geologic guide of the county that fanglomerate was encountered and dug out when the Pier 1 store along U.S. Route 40 was constructed in the last several years.

A pillar inside the National Capitol building in Washington, DC compsed of fanglomerate

Stop 5 Vulcan Materials Quarry – Buckeystown Pike north of Buckeystown (need permission) Frederick formation – limestone – Cambrian age Grove formation – Limestone – Late Cambrian to Early Ordovican Our second quarry of the day is operated by Vulcan Materials Company. According to their website, here is an introduction to Vulcan Materials: “Vulcan Materials Company is the nation’s largest producer of construction aggregates—primarily crushed stone, sand and gravel—and a major producer of aggregates-based construction materials including asphalt and ready-mixed concrete. Our coast-to-coast footprint and strategic distribution network align with and serve the nation’s growth centers. We are headquartered in Birmingham, Alabama.” “Over 300 Vulcan sites produce construction aggregates, and about 200 facilities produce asphalt and/or concrete, which also consume aggregates. All of these are located in the U.S. except for our large quarry and marine terminal on Mexico’s Yucatán Peninsula. The products from this facility are primarily exported by ship to the U.S. Gulf Coast, where quality stone cannot be mined locally For more information on this company go to www.vulcanmaterials.com.” “What we produce is used in nearly all forms of construction. In particular, large quantities of aggregates are used to build and repair valuable infrastructure such as roads, bridges, waterworks and ports, and to construct buildings both residential and nonresidential, such as manufacturing facilities, office buildings, schools, hospitals and churches.” Here the limestone is used primarily for aggregate purposes, for asphalt roads, concrete roads, road base, lightweight block, rip-rap for slope stabilization, stone driveways, construction, etc. The basics of the operation is laying out blasts or shots, blasting rock, loading rock into haul trucks to take to the plant where the various rocks are crushed, screened, and separted into their appropriate sizes. Of course, knowing the geology and having a good mine plan are also important. At one time the rock was mined for use to make cement, however the chemistry is not quite high enough in calcium carbonate as Essroc like so they don’t get rock for that purpose any longer. Some customers use the rock for out of spec AG lime. Two limestone formations occur in this area. The Frederick formation is found within the quarry while the Grove formation lies to the east. Based on stratigraphy of these formations, each limestone unit can be divided further into members. From west to east, they are: Rocky Springs Station member, Adamstown member and Lime Kiln member, all belonging to the Frederick formation. The Grove formation can be divided into the Ceversville member and the Fountain member (west to east). You will be permitted to collect off of a pile of limestone here. Watch for white, yellow or other colors in veins or crystals. This will be calcite, the primary mineral that composed limestone. It has a hardness of 3 on the Moh’s Hardness Scale, has 3 directions or cleavage and forms rhombohedra or dog-tooth shaped crystals. Calcite will react with vinegar with made into a powder or more readily with muriatic acid.

Aerial geologic map of the Buckeystown quarry

Stop 6 Catoctin (Isabella) Furnace in Cunnigham Falls State Park near Thurmont 18th and 19th century iron furnace The historical marker states: ”Catoctin Furnace: An important iron furnace during the Revolution owned by Governor Thomas Johnson and his brothers. Furnished 100 tons of shells used at Yorktowne.” The Johnson Furnace was a cold-blast operation. It operated from 1776 to 1795, and then was idle until 1803. The furnace operated again between 1803 and 1811 with substantial improvements. Early production consisted of household implements, tools, cast iron stoves, etc. The works were purchased by by John Brien in 1831 and modernized. The furnace operated until it was shut down and dismantled in 1880. The site of the Johnson stack was probably in about the middle of the retaining wall behind the existing (Isabella) stack. Another owner built the Isabella Furnace in 1856. Both the Johnson and Isabella stacks were 33 feet high, but the Isabella was supplied with a steam-powered hot blast mechanism. The Isabella operation was a advanced design for a charcoal furnace. It might have been capable to use anthracite or coke, but neither were available. The Isabella is the remaining stack on display. A third stack, the Deborah, was built in 1873 about 140 feet south of the Isabella. It was a water or steam-powered hot-blast furnace which used coke or coal with a daily capacity of 35 tons of pig iron. It operated until 1903 and was then dismantled. In the late 1800’s, when the complex was at its heyday it consisted of: 80 houses for workers, a saw mill, a grist mill, a company store, farms, an ore railroad and 3 furnace stacks. Production was 9,000 tons of pig-iron annually. A magnetite (iron) mine was located on a hill to the southwest and continued to mine until 1912. Today, we should have time to visit the stack area and walk east to see the remains of the ironmaster’s house. Further walking on the trail will take you past slag heaps a raceway and dam for the waterwheel for the Johnson furnace.

Portal of the Catoctin Furnace

With winter upon us and the loss of foliage and underbrush, now is a great time to go into the woods and explore the Earth. Yes, it is true that animal activity is not as common as it is in the warm months, and there are no flowers showing off their colors on the floor of the forest. But you can see more details in rocks and find them without crawling through a thick understory. And the best part of winter? Reptiles are dormant and are not using the rocks for a heating pad. I conduct most of my field work at this time of year for the reasons above, but use common sense with hunting season going on.

Travel to Gifford Pinchot State Park near Rossville to examine some big boulders that tell an interesting story. Most of the park is underlain with an igneous rock known as diabase. This rock formed from magma but never made it to the surface as lava. Deep within the Earth the magma cooled and solidified into a rock.

But as you visit Pinchot, watch for rounded rocks, some of which may be weathered in an orange hue.

One particular location to walk to is Toboggan Run, located about half a mile west of the entrance on Alpine Road. Walk a “Jeep” trail up a gentle hill and off to the right, and you will notice rounded boulders. In the early years of this recreational property, the state constructed a toboggan run for local residents to enjoy during the snowy months. Although only the concrete piers remain today, I can only imagine the many thrills that were enjoyed here by many families. On the other side of sledding here, I know how hard diabase is and hitting it after a toboggan accident can be painful.

Diabase boulders are Tobaggon Run at Pinchot State Park

Look at the large exposure and think about how the rock was formed. Look at the crystals in the rock. These minerals formed from magma deep within the Earth. Some of them formed quickly; others formed as the magma cooled. Although the size of the crystals can barely be seen by our eye, they are large enough to see. This evidence tells us that the magma cooled rather slowly, relatively speaking. If the magma cooled quickly, the rock would have a fine-grained appearance with no visible crystals. Conversely, if the magma cooled very slowly, large crystals (like those seen in granite) would have formed.

Imagine two to four miles of crust over your head. That’s approximately how far beneath the Earth’s surface magma was when diabase formed. Geologists can determine that by the texture and composition of the rock. Just what happened to all of this material to now have the diabase on the surface?  It is the same two agents affecting our surface today known as weathering and erosion. The diabase is about 160 million years old. Since that time, our part of the Earth has seen major episodes of weathering and erosion. All of this material has been removed and transported into streams, the Susquehanna River, Chesapeake Bay and continental shelf.

Look at the surface of the rock. You will see patterned cracks passing through the diabase. These are cooling cracks caused by cooling of the magma. The same applies on a baseball field after rain.  Where you have a puddle of water lying, the dirt will crack as the water evaporates or soaks in and dries. Weathering is accelerated along these weak areas as rain gets inside and vegetation grows.  Over time, small pieces of this dense rock are broken off of the bedrock, and it eventually takes on a rounded appearance. Can you see any pieces just about ready to become dislodged from the bedrock?  The rounded appearance is known as spheroidal weathering, a trait characteristic to igneous rocks and particularly diabase. Have you ever visited the classic site for diabase at Devil’s Den on the Gettysburg National Military Park in Adams County or the Governor’s Stable near Falmouth in Lancaster County? These are two other great diabase sites.

Diabase boulders showing cooling cracks and spheroidal weathering.

Our second stop is at Rocky Ridge County Park in Springettsbury Township. The first county park in York County, this 750-acre park has a lot to offer. Hiking, horseback-riding and mountain bike trails are well marked and, the park has two magnificent overlooks where visitors can take in the landscape. Rock in the park is largely a conglomerate of sedimentary rock containing rounded pebbles. Most of the pebbles are quartz in composition, with some darker pebbles composed of the volcanic rock known as rhyolite. Because the Hellam Hills are the source of the rhyolite, these fragments are more angular in shape. The rock known as the Hellam Member of the Chickies Formation is believed to be about 550 million years old and was formed in a channel of a river or in a delta environment. This is one of the oldest sedimentary rocks in Pennsylvania.

At the north overlook about 700 feet northwest of the Oak Timbers Parking Area is a wonderful outcrop of the conglomerate.   Since quartz is rather resistant to weathering, but these pebbles are well rounded, geologists estimate that the source was 40-50 miles away, probably to the south or southeast.  Also note that the quartz pebbles stick up from the rock matrix.  This tells us that the quartz is more resistant to weathering than the minerals making up the rock.  Walk down the trail past the overlook and you will easily spot loose quartz pebbles that have been eroded from the rock over the years.

View from the North Overlook at Rocky Ridge County Park

Located along the northern boundary of the park almost halfway between the Oak Timbers and Hidden Laurel picnic areas is a nice exposure of the conglomerate that features a flat rock and several rock shelters. When you stand on the flat rock, you are standing on a delta or river channel surface that dates back 550 million years. Quartz pebbles sticking up above the rock provide good traction.

Conglomerate containing quartz pebbles and a rhyolite pebble

The rock shelters are a product of weathering. Natural caves do not occur in conglomerate, but with the speed of weathering varying from layer to layer, little shelters do form. Although there is no evidence of prehistoric activity here, some rock shelters in York and Lancaster counties were used by people thousands of years ago. Search through the Rocks Beneath Your Feet archives to read about the rock shelters in the Caledonia Park area.

Remember the rock diabase introduced at Pinchot State Park?  Well, there is diabase in Rocky Ridge County Park. Should I keep you guessing and let you find the rusty orange pieces of the rock lying on the surface along one of the trails?  Perhaps I could offer a prize to the first person to report it to me! 

I’m not the type of person to leave you hanging, so here we go. Walk toward the southern boundary of the park on Trail 6 out of the Hidden Laurel picnic area. After crossing the creek and walking through a beautiful valley, look for the diabase rocks laying along the trail. They can be passed over rather easily. Different from Pinchot State Park, the diabase does not occur in a large body but is formed in what geologists call a dike.  A dike is an intrusion only about 20 feet wide, but it can extend for miles across the landscape. 

This particular dike is known as the Stoney Brook dike and is named for its excellent exposure in the railroad cut along Pleasant Acres Road just off East Market Street. This exposure was the subject of a previous past blog post. This dike begins in northern Maryland and passes through Loganville to Stoney Brook.  It continues north through Rocky Ridge County Park, under the Codorus Creek at Codorus Furnace, across the Susquehanna River at Haldeman Riffles and terminates nearElizabethtown.

Although it is mapped crossing through Rocky Ridge County Park by George and Anna Stose, it is hard to trace. In fact, I have observed only a few small pieces of diabase along the main rock near the drive into the Oak Timbers picnic area. Even a search of diabase along the power line did not reveal any of the rock.  Now there is a challenge for you during the winter months.

Stose and Stose (1939) geologic map of Rocky Ridge County Park. THe red line represents the Stoney Brook dike and the blue dotted pattern is the conglomerate.

The diabase was formed about 160 million years ago as Pangaea was nearing its separation into separate continents. Just like taking a block of clay and pulling it apart in opposing directions, a large gap forms in the middle of the block and extension cracks toward the out edges of the block.  This same principle occurred with the breakup of Pangaea during the Mesozoic Era. Magma migrated up into these gaps and cracks to “heal” the earth, forming diabase. Pinchot State Park was in the “heart” of the separation while the Stoney Brook Dike and Rocky Ridge County Park were among the extensional fractures. After all, remember the conglomerate at Rocky Ridge Park is about 400 million years older and way before the origin of Pangaea.

If any reader has an idea for a blog post or wants to learn something about something local in geology, please let me know.

This blog is about the Pigeon Hills in western York County.  Pigeon Hills lies between Thomasville and Hanover and is one of the two highland areas in York County lying within the Uplands Section of the Piedmont physiographic province.  The other similar highland is the Hellam Hills located east of York.  The oldest rocks in this highlands are volcanic rocks belonging to the Catoctin Formation.  In the Pigeon Hills, metabasalt is found.  This rock is believed to be over 600 million years old and originated as lava.  Overlying the Catoctin Formation are the Chickies Formation (quartzite), Harpers Formation (phyllite), and the Antietam Formation (quartzite and sandstone).  The Antietam Formation is about 600 million years old.

The Pigeon Hills is a fascinating highlands to study geology.

This blog will visit some of the neat geologic sites in the Pigeon Hills.

Stop 1 – Glatco Lake on Glatco Lake Road. Imagine being here 130 years ago when this lake was a striving iron mine.  Chance were good if you lived in the area, you were either personally connected or somehow related to a mine, furnace or foundry.  At its peak around 1874, York County had 170 iron mines, five furnaces (which were drawing to a close) and numerous foundries.  Pigeon Hills contained about 20 iron mines, all located on the southern slope of the hill.  Most of the mining operations took place between 1850 and 1880.  All of the deposits mined limonite (an iron-oxide mineral). Most of the ore was mined out of the ground, lying loose, not requiring “hard rock” mining, but washing.  The ore was either hauled by a narrow gauge railroad or cart to Smith Station or Kauffman Siding, near Jacob’s Mill.  Some of the ore was used in Mary Ann Furnace, located on the property of Codorus State Park.

A self-guiding sign post to mark one of the Pigeon Hills geology tour. THis sign is at Glatco Lake, a former iron ore mine.

Stop 2 – Nectar Spring on Moulstown Road.  Ground water is found everywhere beneath the earth’s surface.  In most cases, ground water surface reflects the topographic expression.  Several characteristics of bedrock depend on how ground water flows through the earth’s crust.  Porosity is the percentage of pore space in a rock, which allows water to flow through the rock.

The second characteristic is permeability, the ability for a rock to transmit fluid through itself.  If a rock, like sandstone, has uniform grain size, the rock would most likely have a better permeability than a conglomerate. A conglomerate contains various sized particles from anything about 2.5 inches to as small as sand-sized grains.  In this case, the water finds its way through the pores instead of simply following a “tunnel” through the rock.  When ground water intersects the surface, it is called a “spring.”  The Nectar Spring is located in the Chickies Formation  The rock is predominantly quartzite (matamorphosed sandstone).  The rock generally has good permeability and good porosity.  Most springs found in the Pigeon Hills are actually along faults, a natural crack in the crust of the earth that water can easily flow through.

Stop 3 – Pulpit Rock just off of High Rock Road.  This stop brings you close to the highest elevation in the Pigeon Hills.  At an elevation of 1240 feet, you are at the second highest point in York County.

The Chickies Formation is exposed at Pulpit Rock.  Named from the famous Chickies Rock along the Susquehanna River in Lancaster County, this is one of the oldest sedimentary rock formations in Pennsylvania.  Once sandstone, this rock has gone through several stages of heat and pressure (metamorphism) with crustal plate collisions.  With each stage of metamorphism, the quartz grains in the rock were melted and enlarged.

Fossils found in this formation tell geologists about the environment in which the rock was originally formed.  Scolithus tubes are evidence of an animal that once lived in very shallow ocean water close to a beach.  Although the actual work has never been observed, we found the “homes” of these worms.  This fossil is known as an index fossil, meaning that the organism only lived perhaps 20-30 million  years.  Scolithus gives us a date of 600-570 million years old.

Stop 4 – Metabasalt along Beaver Creek Road.  The oldest rock in the area is known as metabasalt.  Metabasalt was once volcanic lava dating over 600 million years old. The actual volcanic mountains or vents have been eroded away or destroyed during times of the shifting earth.  These rocks were believed to be over 800 million years old, but recent techniques in dating rocks have shown the metabasalt to be 200 million years younger.

The word “meta” is used in front of the word basalt since the rock has gone through several stages of heat and pressure.  These stages of metamorphism have altered the original mineral composition of the rock.  The greenish color of the rock is from the mineral chlorite.  Other minerals found in the rock include epidote, hornblende, pyroxene and quartz.  The “layering” appearance you may see in the road cut is due to the metamorphism.  The minerals have been aligned perpendicular to the direction of the stress.  An occasional cavity in the rock is a relic of a gas bubble in the lava, not yet filled-in with other minerals.

A closer view of the metabasalt showing cavities which were gas bubbles in the 600+ million year old lava.

Stop 5 – New Oxford Fanglomerate at the intersection of Maple Grove road and Beaver Creek Road.  This is the youngest rock examined in the Pigeon Hills.  Some place in the short distance you drove from the metabasalt exposure to this area was an imaginary line that divides rocks about 600 million years old to those only about 200 million years old.  Imagine that, there is 400 million years of the earth’s history missing.  Geologists call this an unconformity, a gap in geologic time.

The New Oxford Formation fanglomerate at the north end of Beaver Creek Road.

These rock are the first rocks laid down in a totally different environment than those rocks in the Pigeon Hills.  About 200 million years ago, we were located where southern Florida is today.  In fact, our climate and appearance was similar to that of the Everglade Swamp.  Abundant rain and vegetation and tropical temperatures dominated our area.  Small meandering streams and oxbow lakes were common.  With some luck, you might have caught a glimpse of a reptile or dinosaur walking across the landscape.

The rock here is known as a fanglometate.  Examine the pebbles in the rock.  Are they rounded or angular?  What composition do you think the pebbles are?  Well, the pebbles are angular in shape, meaning that they were transported in water a very short distance.  Many of the pebbles are identical to the quartzite of the Chickies Formation found at Pulpit Rock and on the higher elevations of the Pigeon Hills.  There are also some limestone fragments similar to the rock found in the valley south of the Pigeon Hills.  Geologists call this rock a fanglomerate.  It was here that a stream running off the PIgeon Hills carried these large rock fragments down onto the valley floor of the “everglades.”  Where the water speed decreased, the stream had to drop the larger fragments, thus forming an alluvial fan.  This fanglomerate forms a very narrow discontinuous band across York County, marking various 200-million year old streams flowing in the ancient Everglades.

As you can see just within a small area since as the Pigeon Hills, geology can be diverse.  By the story is not quite over.  Now that you have a simple understanding of what is in the Pigeon Hills, let’s finally and briefly describe where this highland came from.  If you would do a search where the Catoctin Formation is found in Pennsylvania, you will see that its largest area is within South Mountain.  Matter of fact, the southern extension of South Mountain is known as Catoctin Mountain in Maryland, from which the rock unit is named.

Folding in the rock near Jack’s Mountain Tunnel, the area that the Pigeon Hills is believed to have broken away from South Mountain.

In the early 1990’s, geologists doing research in South Mountain close to the Mason-Dixon Line came to the conclusion that the Pigeon Hills (as well as the Hellam Hills east of York) are broken-off pieces of the Earth’s crust.  It is now believed that during the mountain-building episode known as the Alleghenian Orogeny when Africa and North America collided; both the Pigeon Hills and Hellam Hills were detached and transported along a fault to their present-day location.  The area of detachment is believed to be In the Jacks Mountain area near Carroll Valley, Adams County.  That would explain the similar geology the Hellam Hills, Pigeon Hills and South Mountain have.  Enjoy your tour!!!!

This post is a primer for individuals who want to examine some interesting geology. We’re concentrating today on the Gettysburg area, including South Mountain to the west. The first stop is Valley Quarry – Gettysburg Plant, which is an active operation. With permission and work schedules, the quarry allows mineral collectors access to the quarry on Saturday mornings. (Anybody with questions or comments can contact me at jonesgeo@comcast.net. Enjoy the trip!)

STOP 1.  Valley Quarry – Gettysburg Plant

One wall at Valley Quarry showing diabase (dark), which heated and baked the sedimentary rocks, turning them into a hornfels.

• The quarry was previously known as John S. Teeter and Sons, Inc. and Harry T. Campbell Sons Corp.
• The rock here is used for paving projects that require a more resistant wearing aggregate, among other uses.
• Exposed rock areas in most of the quarry are the lower beds of the Gettysburg Formation, known as hornfels, a metamorphic rock.
• These rocks were originally mudstones, siltstones and sandstones laid down in a tropical climate; there is some evidence of evaporates in the samples.
• In the western highwall, diabase (an igneous rock) is exposed. This is the lowest part of a diabase intrusion that is about 1,800 feet thick and dips toward the northwest.
• This rock is classified as belonging to the York Haven Diabase.
• Diabase is very dense and cooled from magma at least a mile or more beneath the surface (intrusive).
• The diabase cannot be used by the quarry due to its hardness.
• Magma intruded into the sedimentary rocks and baked the sandstone, siltstone and mudstone into hornfels (heat only – known as thermal metamorphism or contact metamorphism).
• This intrusion is known as the Gettysburg Sheet and is classified as a sill.
• Temperature of the magma was about 1,100 degrees C.
• The light, tan-weathered, greenish rocks suggest a higher carbonate-rich rock.
• Cross-bedding, channels and remnants of evaporate minerals suggest a playa (beach-like or seasonal lake) environment.
• High-temperature minerals identified here include: actinolite, andradite, grossular, diopside, tourmaline and tremolite.
• High-temperature minerals identified here include: actinolite, andradite, grossular, diopside, tourmaline and tremolite.
• Medium-temperature minerals identified here include: apatite, bornite, chalcopyrite, chlorite, copper, djurelite, epidote, feldspar, quartz, hematite, magnetite, mica, pyrite, rutile and titanite.
• Low-temperature minerals identified here include: calcite, chabazite, heulandite, natrolite, stilbite, stilnomelane.
• Weathered minerals identified here include: chalcanthinite, chalcocite, chrysocolla, cuprite, dioptase, goethite, malachite, montmorillinite, opal, pyrolusite, selenite and sericite.

STOP 2. Plum Run Bridge – Confederate Avenue, Gettysburg National Military Park

An example of an Atreipus footprint from Trostle Quarry.

• Rocks used here were taken from Trostle’s Quarry along Bermudian Creek, 3.3 miles due east of the U.S. Route 15 – PA Rte. 94 intersection near York Springs, Adams County.
• A total of 57 footprints were removed from Trostle’s Quarry in the 1930s.
• Rocks here include sandstone and siltstone belonging to the Heidlersburg Member of the Gettysburg Formation, dated at about 210 million years ago.
• Footprints of four species of dinosaurs can be seen in selected blocks on top of the bridge.
• The condition these footprints or handprints depends heavily on the material in which the dinosaurs stepped. Prints in a sandy texture are not as well-preserved as those in the siltstones.
• Other sedimentary features, including ripple marks and desiccation (mud) cracks, can be seen in some of the blocks.

POINT OF INTEREST A – Devil’s Den and Little Round Top, Gettysburg National Military Park

Unique weathering of the diabase on the slope of Little Round Top

• This is the classical exposure of diabase. Walking through this rock outcropping, you will see many features that occurred during the formation of the rock from magma.
• Features include cracks caused by magma that cooled at different rates.
• The diabase, through weathering, has become rounded in shape — a process known as spheroidal weathering. Though magma never reached the surface here, the magma cooled into the diabase. This occurred perhaps one to two miles below the surface. Weathering and erosion evidently brought the rock to the surface.
• Because diabase doesn’t create a thick soil, soldiers could not trench for defense. They had to rely on these boulders or build diabase stone fences for protection.

STOP 3. CSX Railroad Cut – Lee’s Headquarters

Sandstone exposed in the CSX Railroad cut

• Approximately 110 feet of reddish shale and sandstone exposed here belong to the Gettysburg Formation. Notice the thin bedding of the shale and the thicker bedding of the sandstone.
• The bedding dips 24 degrees to the northwest. These rocks are basically lying in their original position since no major tectonic events have affected them.
• The reddish color of the rock is due to oxidation of iron, as the sediment was occasionally exposed to the air following deposition.
• Walking east along the tracks, notice the change of color in the rock.  This is another example of hornfels (similar to Stop 1).  A diabase intrusion is located behind the gabion fence.  Diabase can be seen at the junction of the sidling and main line, as well as in the south bank along the main line.
• This intrusion is known as a dike and measures 92 feet thick, and dips 50 degrees southeast.
• Notice the size of the crystals in the diabase.  Are they small (micro) or large? The crystals in this diabase are micro, indicating that the magma cooled relatively quickly.
• Think about granite with its large crystals.  This indicates a slower cooling period.
• Before the railroad cut was modified with false walls, this was the best geologic exposure showing a diabase intrusion in southeastern Pennsylvania.
• A small amount of copper (malachite) was found at the diabase-hornfels contact.
• Several large copper and iron mineral deposits were formed in this same manner, i.e. Cornwall Iron Mines (Lebanon County), Dillsburg Iron Mines (York County) and Stone Jug Copper Prospect (Adams County).

Diabase exposed in the CSX Railroad cut. The diabase dike is shielded by the man-made rock wall.

POINT OF INTEREST B – Carbaugh-Marsh Creek Fault

• As we enter South Mountain on U.S. Rte. 30, we are driving on the Carbaugh-Marsh Creek Fault. This fault formed as a result of the great African-North America collision ~325 million years ago, during what we call the Alleghenian Orogeny.
• Viewed from a satellite photograph, one can see the fault. South Mountain north of U.S. Rte 30 has been shifted ~3 miles further west than the south side.
• Within a fault, the rock gets broken from the movement, which accelerates the weathering and erosion process. The gap is a result of this faulting and erosion.
• The Confederates used this gap to head to Gettysburg from near Chambersburg.

Satellite photograph of South Mountain (in the middle). Notice how the northern portion is offset to the left (west) relative to the south half. The Carbaugh-Marsh Creek fault is to blame for this offset.

POINT OF INTEREST C – Catoctin Metarhyolite

• From Lion Club Park to the intersection with Pa. Route 234, metarhyolite is exposed along U.S. Route 30. A nice outcrop of this volcanic rock is seen just east of the intersection with Route 234.
• Metarhyolite has undergone some metamorphism, hence the “meta” in front of the rock’s name.
• The word “catoctin” is the proper name for this formation; it is named for its fine exposures in the Catoctin Mountains in Maryland.
• This rock and its associated volcanic rock, metabasalt (oceanic rifting) are related to the breakup of a super continent known as Rodinia about 600 million years ago. The metarhyolite has been dated to about 570 seven gears ago.

Rhyolite exposed in South Mountain. Horizontal white lines represent individual flows of lava some 560 million years ago.

STOP 4.  Buchanan Valley Fire Department-Metarhyolite Exposure

• Metarhyolite is composed mainly of orthoclase feldspar and quartz.
• This rock formed on the edge of Rodinia as the supercontinent rifted apart (continental rifting).
• Rhyolite has the same minerals as granite, however it cooled faster than granite forming the smaller-sized crystals.
• This rocks belongs to the Catoctin formation of Proterozoic age
• As you walk this small exposure, look for rhyolite that might have flow lines or some indication of lava flows.

STOP 5. Potato Road – The Border Fault

The Border Fault runs in the valley below the housing development and divides marks the boundary between South Mountain and the Piedmont province.

• This valley represents the border between rocks of South Mountain (from about 600 million years ago) and rocks of the Piedmont Gettysburg-Newark Section (from about 200-170 million years ago). We are standing on the older side.
• This fault was active in at least the Mesozoic Era as Pangaea was rifting apart.
• This is the western side of what is called the Gettysburg-Newark Basin, a down-warped piece of crust. The Basin was filled with eroded sediment and, later, the intrusion of magma, which protruded up through the rifting crust.
• Quaker Valley is a valley because the rocks in a fault area have been previously fractured and crushed, which allowed quicker weathering and erosion.

STOP 6.  Main Street, Bendersville Road Cut – Aspers Basalt

A sample of Jurassic age basalt, a rare rock from the Pennsylvania Piedmont. Gently dig into the road bank for samples.

• Most magma that intruded into rocks in the Triassic period and before cooled inside of the earth as the rock diabase.
• All of these intrusions are Jurassic in age.
• The Aspers Basalt is the only evidence in this region that there was an actual lava flow — a very small flow, but it did exist.
• There might have been additional flows, but these could have been eroded away.
• This exposure shows just how difficult it can be for a geologist to interpret the geology. This rock is concealed and can be found only when you dig into the hillside or walk into the orchard.
• Look for a light-brownish rock that is pitted with cavities. These cavities were “gas pockets.”

STOP 7.  Chestnut Hill Diabase Intrusion – Earthquakes

• Chestnut Hill is underlain with Jurassic-age diabase, similar to that in the CSX Railroad cut.
• Diabase is a very dense rock, weathering in a rounded (spheroidal) shape.
• Here, the diabase intruded through the Gettysburg Formation sedimentary rocks.
• On May 26, 1994, an earthquake was recorded in this area. The tremor had a magnitude of 2.8 with a depth of 11 km.
• With no seismographs in the immediate area, its location is not exactly known, perhaps within 5 kilometers of Chestnut Hill.
• The closest seismographs are located at Soldier’s Delight State Park near Owings Mill, Md., and Millersville University in Millersville, Pa.
• Earthquakes do occur within the Gettysburg Newark Lowlands Section, but are not common. However, if an earthquake risk map would be prepared of the area, the contact between the diabase and the surrounding sedimentary rocks would be a point of concern.
• An earthquake that occurs within the diabase will occur along this contact due to the area of less resistivity of the rock.
• Dillsburg, in York County, has experienced about 3,000 tremors since October, 2008. These tremors are occurring along this contact about 1 mile in depth.

FURTHER READING

Baird, D., 1993.  Appendix B: The Trostle Quarry footprints and their makers in Britcher, R., editor, Guide Book for the 12^th annual field trip of the Harrisburg Area Geological Society, Harrisburg, PA.

Brichter, Raymond W., editor, 1993.  Guidebook for the 12th annual field trip of the Harrisburg Area Geological Society: South Mountain and the Triassic in Adams County, Harrisburg, PA.

Faill, R.T., 2004.  Earthquake catalog and epicenter map of Pennsylvania.  Pa. Geol. Survey, 4^thser.,  Map 69.

Fleeger, G.M., 2008.  Geology of the Gettysburg Mesozoic Basin and Military Geology of the Gettysburg Campaign.  73^rd Field Conference of Pennsylvania Geologists, Gettysburg, PA.

Jones, J.L., and Eisenberger L., 2006.  A Tiny Look at a Large Quarry: The Micromineralogy of Valley Quarry, Gettysburg, Pennsylvania.  Rocks and Mineral Magazine, May/June, v. 81, no. 3.

Scharnberger, C.K., 2003.  Earthquake Hazard in Pennsylvania.  Pa. Geol. Survey, 4^th ser., Educational Ser. 10.

Shultz, C.H., 1999.  The Geology of Pennsylvania.  Pa. Geol. Survey and Pittsburgh Geol. Society, Special Publication 1.

Shirk, W. R., 1980. A guide to the geology of south central Pennsylvania. Obson & Kays, Inc, Inc. Chambersberg, PA.

Smith, R. C., II, 1975. Geology and geochemistry of Triassic diabase in Pennsylvania. Geol. Soc. America Bull., v. 86, p. 943-955.

Smith, R.C., II,, Berkeiser, Jr., S.W., and Barnes, J.H., 1991. Pennsylvania’s Version of he Catoctin Metabasalt Story in 56th Annual Field Conference of Pennsylvania Geologists Guidebook – Geology in the South Mountain Area, Pennsylvania, William Sevon and Noel Potter, Jr., editors.

As you might have learned by now, I strongly encourage folks to investigate local history and geology. As I teach my students, you can read all the geology textbooks you want, but to really understand what the Earth is doing, the best teaching method is go out and look at it. If I had it my way, I would have geology students on a field trip every week for our laboratory exercises.