Research • Education • Outreach
“We Look Into the Past”
Jones Geological Services
(717) 887-7103
Email: jonesgeo@comcast.net
Research • Education • Outreach
“We Look Into the Past”
Jones Geological Services
(717) 887-7103
Email: jonesgeo@comcast.net
Geology does not stop at a political or natural feature. In this case the Lowlands Section of the Piedmont province advances into Adams County. The physiographic section is well known for its limestone and dolomite resources. The area is also known to geologists as a very complex area containing folding and faulting. To the left is a picture of a fault exposed in the Vulcan Materials quarry. If you look carefully, you will detect displacement along the fracture and see calcite in the fault zone. Nice calcite crystals are still being found today as Vulcan Materials is a very active operation. However, collecting is not permitted by the quarry.
Although found from the Bethlehem Steel Company quarry (now known as Vulcan Materials quarry north of Hanover, this American mastodon manibal was found in a sinkhole in the early 1970’s. Other bone material of mastodons have been recovered over the years at the quarry.
This rock of Triassic age is found in a roadcut along Pa. Rte. 194 at the intersection with Maple Grove Road south of Abbottstown. Notice how angular the rock fragments are? Their shape tells a geologist that the fragments were not transported far in water. The fragments are reddish sandstone, quartzite and rarely a piece of limestone. With angular fragments, the rock is termed a breccia.
Sinkholes are common I areas underlain with limestone. This sinkhole is located on the north side of Oxford Ave opposite the Vulcan Materials Quarry. Sinkholes have caused property damage through the limestone regions of Pennsylvania.
This is the north wall of the Vulcan Materials Quarry, the largest quarry in Adams County. The quarry is extracting limestone and dolomite for road construction, cement and flux material. Try to trace layers of the rock across the picture and you will detect how deformed these rocks are in the Piedmont Lowlands Section. The rocks have been folded and broken by several crustal collisions.
Devils Den is the classic exposure of the igneous rock known as diabase. Possibly forming 4-5 miles beneath the surface of the Earth, today diabase is at the surface because of its resistivity to weathering and erosion. Notice how the rock is in a rounded shape due to the weathering. This is called Balanced Rock. If you visit the site, walk in under the rock and look to the left where the top and side rock meets. There are two white marks on each rock that line up with each other. If you ever see these marks offset, one of these rocks has recently moved.
This is the CSX Railroad cut behind Lee’s Headquarters. This exposure is excellent to see what the rocks underlying the battlefield look like. The closest reddish-brown rocks are sandstone and shales belonging to what we call the Gettysburg Formation. The rock behind the gabion walls is diabase. The dark gray rock in the middle is known as hornfels. As magma intruded up through the shale and sandstones, the heat of the magma baked the rock. The cut is best viewed from the field behind Lee’s Headquarters.
This drawing completed by Roger Cuffey, retired professor of vertebrate paleontology from Pennsylvania State University shows the various rock slabs on the Confederate Ave bridge over Plum Run on the Gettysburg Battlefield. The rock was quarried from Trostle’s Quarry in Reading Township, Adams County. Please do not harm the foot prints with any tools. Only look and photograph.
An Atreipus foot print and hand print as seen on the Confederate Ave bridge on the Gettysburg National Military Park. This slab is located on the north side of the bridge.
Township These two mine shafts are the only such openings remaining in this area that represents the once major copper district. A number of copper mines are found in this region and was one of the leading copper districts in the United States in the late 1800’s into the early 1900’s. This is the Reed Hill Mine along Copper Run. Many of the abandoned mines are now on the property of Michaux State Forest.
A sample of native copper in quartz found within the basalt in the Copper Run area north of Gladhill. Copper was mined from this area from the mid 1800’s into the early 1900’s. Many of the visible prospects are now on the property of Michaux State Forest.
This is a classic example of a diabase dike intruding older rocks in the Balley Quarry at Fairfield. Diabase is an igneous rock formed inside the Earth. A crack in the crust allowed the magma to migrate up through the limestone to fill in the fracture. The dike is about 15 feet wide.
The age of the limestones in the Valley Quarry at Fairfield has been debated for some years. Some geologists thought the limestone correlated with the Early Paleozoic e limestones in the Great Valley under Hagerstown, MD and Chambersburg. Others thought the rock was Triassic in age, matching those rocks surrounding Fairfield. In 2011, members of the Franklin County Rock and Mineral Club discovered dinosaur footprints while on a fieldtrip to the quarry. This is a Grallator footprint. This find placed a Triassic age on the age exposed in the quarry
Township These two mine shafts are the only such openings remaining in this area that represents the once major copper district. A number of copper mines are found in this region and was one of the leading copper districts in the United States in the late 1800’s into the early 1900’s. This is the Reed Hill Mine along Copper Run. Many of the abandoned mines are now on the property of Michaux State Forest.
A sample of native copper in quartz found within the basalt in the Copper Run area north of Gladhill. Copper was mined from this area from the mid 1800’s into the early 1900’s. Many of the visible prospects are now on the property of Michaux State Forest.
This is a classic example of a diabase dike intruding older rocks in the Balley Quarry at Fairfield. Diabase is an igneous rock formed inside the Earth. A crack in the crust allowed the magma to migrate up through the limestone to fill in the fracture. The dike is about 15 feet wide.
The age of the limestones in the Valley Quarry at Fairfield has been debated for some years. Some geologists thought the limestone correlated with the Early Paleozoic e limestones in the Great Valley under Hagerstown, MD and Chambersburg. Others thought the rock was Triassic in age, matching those rocks surrounding Fairfield. In 2011, members of the Franklin County Rock and Mineral Club discovered dinosaur footprints while on a fieldtrip to the quarry. This is a Grallator footprint. This find placed a Triassic age on the age exposed in the quarry.
Along the CSX Railroad at the Jacks mountain tunnel is a great exposure of quartzite showing the intense folding that the rocks of South Mountain went through during the collisions that built the supercontinent of Pangaea. Walking the railroad is considered trespassing with permission.
On the Strawberry Hill Preserve is an abandoned quarry where volcanic slate was once removed. A close look at the rock shows crenulations which are small folds in the rock, reflecting the intense movement and pushing up of South Mountain during the Alleghanian Orogeny when Africa and North America collided 325-260 million years ago.
Ski Liberty is a popular ski resort in the winter. The rock that forms the mountain is an igneous rock known as diabase. The rock formed deep inside the Earth as magma cooled. As weathering and erosion acted on the surface of our Earth, this rock being very resistant is now forming many of the hills within this area of Adams County. The rock formed during the Jurassic Period as Earth was healing itself after the separation of the supercontinent Pangaea.
This is a sample of basalt, an igneous rock that formed as lava just south of Bendersville. The rock is Jurassic in age and is a rare occurrence in this area. Notice holes on the surface? They were unfilled gas bubbles in the lava.
With a small amount of imagination, one can picture a major fault occurring along the eastern slope of South Mountain. South Mountain contains igneous, sedimentary and metamorphic rocks dating back to about 560 million years ago. To the east the region is known as the Piedmont Gettysburg-Newark Sections which contains sedimentary and igneous rocks formed during the Mesozoic Era (220-160 million years old). If we would dig deep enough along the eastern slide of South Mountain, we would find the contact between these two areas and find a definite line separating the Piedmont and South Mountain. This is known as the Border Fault where the Mesozoic rocks are faulted against the older South Mountain rocks.
Trostle Quary was a rather exciting location to visit in the mid 1930’s as a total of 52 dinosaur foot tracks were found here. The rock is a thick-bedded siltstone and sandstone that formed during the later part of the Triassic Period. The footprints recovered from here are now in several museums and on a stone bridge on the Gettysburg National Military Park.
The Reliance Copper Mine was located just north of Hunterstown and operated during a short span in the early 1900’s. Although a site map of the operation has been preserved, records of mining conducted here is rare. Today only several stone foundations, several dump piles and the filled-in shaft are visible, especially during the winter months. There was a report that gold was recovered from this site which led gold prospectors into the area in 1971, where gold was discovered in nearby Beaverdam Creek.