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
Carroll Township
The first documented earthquake in York County occurred near Franklintown in June, 1997. Three separate earthquakes gently shook the area with the largest recorded at 2.3 on the Richter Scale. From numerous interviews with residents, returned newspaper surveys and knowledge of the local geology and earthquake history within the
Piedmont, this isoseismal map was constructed showing where the greatest shaking was felt. Note the alignment of the IV zone, which parallels a possible fault found as a result of fieldwork following the earthquake. Jeri Jones joined forces with Dr. Charles Scharnberger of Millersville University, and Dr. William Kreiger of York College of Pennsylvania to investigate this event.
One of the most productive iron districts in York County is found about 1.5 miles east of Dillsburg, where magnetite was mined from 10 different mines between 1825 and 1890. This is a recent photograph of the Logan-Longnecker Mine on Ore Bank Road. This water-filled shaft dips to the right at 30 degrees and is about 270 feet deep. Approximately 1.5 million tons of iron ore was removed from this district. The Dillsburg magnetite deposit is one of Jeri Jones’ favorite areas for investigation and is geologic similar to the Cornwall Iron Mine in Lebanon County.
In Dogwood Hollow along Tuckahoe Road, this 1910 photograph shows the striving community that was associated with clay mines. White clay was mined from this area from about 1910 until the 1930’s. Today, a rapid growth in urban development has destroyed several of these mines. During the winter months, many of the old pits, dumps, foundations, and railroad beds can be seen.
Remnants of Manor Furnace which operated between 1842-1868. Found today along Manor Furnace Road and only visible during the winter months.
The New Oxford formation sandstone was quarried on Conewago Mountain for building stone. Not only were large blocks removed for blocks for buildings, but some were also hand-shaped for the production of pillars. The Dauphin County Courthouse has pillars on the front of building made from this area. This specimen still remains along Rohrer’s Church Road and measures six feet long and thirty inches in diameter.
This quartz crystal was recovered from a clay-filled sinkhole at the Codorus Stone & Supply Company quarry.
The crystal is about 4.5 inches long and was formed by surface water moving through silica-rich clay. Numerous crystals have been collected since June, 2001.
Franklin Township
The Mont Alto Member of the Harpers Formation outcrops within the Blue Ridge Section of the Valley and Ridge physiographic province.
The exposure is located along the southern edge of the Camp Tuckahoe Boy Scout Camp. The quartzite here is dipping to the right.
The highest point in York County is located within the Blue Ridge Section of the Valley and Ridge province. A peak to the northeast of Stone Head and southeast of Camp Tuckahoe is at the elevation of 1412 feet above sea level. From this vantage point, one can view several counties. Here, looking south, the rolling landscape of the Gettysburg-Newark Section of the Piedmont is viewed. The most-distant ridge in the distance to the left is located near Pinchot State Park.
From Stone Head, looking north through Little Dogwood Gap, one can see a portion of the Cumberland Valley, the broad valley that separates the Blue Ridge Section (locally known as South Mountain) and the Appalachian Mountain Section (seen in the distance). The Blue Ridge Section terminates just to the right of this photograph near Williams Grove, which marks the northern terminus of the famous Blue Ridge Mountains of Virginia, North Carolina and Tennessee.
Hanover
In areas underlain with limestone and dolomite, sinkholes often form from fissures in the rocks enlarging and finally forming a funnel-shaped depression. Some sinkholes are also created by the failure of a cave roof. Sometimes sinkholes can cause serious damage to buildings or roadways. This road sign is in the vicinity of the Vulcan Materials quarry north of Hanover. The quarry is pumping up to seven million gallons of water out daily, which would also cause a lower water table (thus a void). Over time, gravity will take over even under ground, causing ceiling failure in this cave. Photo courtesy of G. Patrick Bowling, P.G.
Hellam Township
A scenic waterfall in “Accomac Gorge.” The bedrock is the Catoctin Formation metabasalt. Combined with the exposures in the stream and the roadcut just to the south, make this one of the largest exposures of the oldest formation within the Hellam Hills. Metarhyolite is also found in the area. The presence of these rocks prove that volcanoes did occur in York County approximately 700-800 million years ago. Other areas where these volcanic rocks can be found include near the Hellam interchange of U. S. Route 30 in the Hellam Hills and in the Pigeon Hills near Hanover.
In “Accomac Gorge”, the stream shows an evolutionary history of potholes. Here, these potholes are formed within the Catoctin Formation metabasalts.
The most widespread formation within the Hellam Hills is the Chickies formation. One member, the Hellam Conglomerate occupies some of the higher elevations. A conglomerate is a sedimentary rock that contains rounded pebbles. In this case, the pebbles are composed of quartz. The rock is one of the oldest sedimentary rocks in Pennsylvania dating back 570 million years ago. Geologists think that this rock was formed in a delta environment.
Codorus Furnace is one of five iron furnaces that once existed in York County. This furnace located on the east side of the Codorus Creek near the junction with the Susquehanna River has been rebuilt and is currently owned by the Conservation Society of York County. The furnace operated in the late 1700’s into the mid 1800’s processing iron ore mostly removed from the Earth in the Hellam Hills of York and Chestnut Ridge in Lancaster County.
Shull’s Rock provides one of the most scenic pictures of the Susquehanna River in York County. The rock is composed of the Chickies Formation quartzite. Here looking north, notice the railroad bridge in the foreground. In the distance is Brunner’s Island, a coal-generation electric plant. To the right is the Lancaster County Solid Waste facility near Bainbridge. Notice above the railroad bridge a line crossing the river. This is a “riffle” in the water where the Stoneybrook diabase dike crosses into Lancaster County. The diabase is more resistant to weathering and erosion compared to the surrounding rock. Please note, Shull’s Rock is on private property and trespassing will not be tolerlated.
At Shull’s Rock, excellent examples of Scolithus tubes are visible. In this example, these are at the top of the bed (looking down on the tubes). Each circle represents a tube. These tubes are believed to have been formed by a worm boring its way through the sand some 600 million years ago. When a geologist finds these worm tubes like in this case, it helps the scientist to determine which way the beds are oriented. Photo by Mary Ann Schlegel
Chimney Rock is a classic site of the Hellam Conglomerate, the lowest member of the Chickies formation. The rock is over 600 million years old and contains mostly rounded quartz pebbles. Weathering and erosion has formed these two pinnacles over time. This rock is a great teaching tool for structural geology classes. Stretched pebbles and lineations help to interpret the structural geology of the Hellam Hills. On private property, permission has to be obtained from the owners.
Jackson Township
Many of the rocks within the Lowlands Section have been deformed through folding or faulting. Pictured here is the Lower Cambrian-aged Kinzers Formation shale located in a railroad cut southwest of Spring Grove showing excellent recumbent folding. This folding is associated with a nearby thrust fault.
The Lowlands Section of the Piedmont physiographic province is known for its limestone and dolomite resources. This is the largest underground mine in the area, originally known as the Thomasville Stone & Lime Company, now operated by Southdown. Although the operation has been owned by several different firms in the last several years, the quarry today produces mineral resources for a wide variety of products, ranging from ceiling tile filler, pet foods, agricultural purposes, and road construction. Note the tunnel openings in the lower wall.
The Pigeon Hills belongs to the Piedmont Uplands Section. Found between the York Airport and Abbottstown, the oldest rock within the upland is volcanic in origin. The metabasalt has been dated at about 600 million years old. Younger sedimentary rocks overlie the metabasalt. A number of iron ore mines worked along the foothills of the Pigeon Hills in the 19th century.
Lower Chanceford Township
Along the banks of the Susquehanna River at the Holtwood Dam is an exposed of metamorphic rocks. It wasn’t realized by geologists until the early 1990’s that some of these metamorphic rocks actually were metabasalts that were formed along a “mid oceanic ridge” setting during the Early Paleozoic. Some of the metabasalts illustrate pillow structures. Pillows were formed where the hot lava flowed into water, quickly cooling the material.
Peach Bottom Township
As seen from Lancaster County, Slate Ridge is a prominent ridge running about 17 miles from northern Maryland, through York County into Lancaster County. Slate Ridge is underlain by the Peach Bottom formation. Slate within the ridge was extensively quarried from the mid 1700’s into the 1940’s.
Shrewsbury Township
The metamorphic rocks of the Uplands Section in southern York County are complexly folded. Although with seldom-seen continuous rock exposures, this folding is sometimes hard to detect, even to a trained geologist eye. This is one of the nicest exposures showing isoclinal folding. This exposure is found along the Heritage Rail Trail County Park, about 1.5 miles south of Glen Rock. This point can be accessed from either the north by parking at the Glen Rock Parking Area or from the south by parking at the Railroad Parking Area and walking north about 3 miles. Rock is the schist of the Wissahickon Formation, which is interbedded with metabasalts and quartzites. Scale on rock is 6 inches in length.
Springettsbury Township
The Stony Brook dike is one of the best examples of a diabase intrusion into older rock. The dike measures about 10-feet wide here, where it intrudes the limestone of the Conestoga Formation of possible Ordovician age. The dike cut through the limestone during the Triassic Period during the rifting apart of Pangaea.
Springfield Township
The Feigley Bank was one of over 170 iron mines that once worked in York County. The limonite mined here was hauled to Glatfelter’s Station, where it was transported by rail to numerous iron furnaces. This mine operated from about 1785 until the 1840’s. According to scuba divers, the water depth is about 70 feet deep.
Harpers Formation phyllite is well exposed at Nixon County Park near Jacobus. Not only do nice exposures of the phyllite occur within the park, but the park also hosts a self-guided geology trail. Photo be Bill Greenawalt
West Manheim Township
One of the few good exposures of the Marburg formation is found along Grand Valley Road near Long Arm Dam. The Marburg formation is composed of schists and quartzites and is a member of a complex large metamorphic terrain in southern York County. The rock originated as sediment of an ancient ocean known as the Iapetus Sea that covered this area during the Early Paleozoic.
Ground water is a valuable resource. Many households rely on groundwater for their domestic use. This township made a wise decision in 2005 by having a groundwater survey conducted to see if rapid growth in development will affect the groundwater system.
West Manchester Township
Environmental Resource Manager David Hopkins of LWB talks to a group of students about how quarries operate, what they quarry and manufacture and problems they encounter. Here David holds a 2-foot long drill core taken from the floor of the quarry.
Faulting within the Piedmont Lowlands Section is very common. Here at York Building Products – Westgate Quarry, several faults are seen in the walls. If you cannot spot the fracture, trace the line from the upper left to the lower right of the picture. For scale, the height of the wall in this picture is 40-foot.
Wrightsville Borough
Remains of numerous limestone kilns are located at the north end of the borough along Front Street. These kilns were constructed and used by J.E. Baker Company. The limestone used for the kilns was quarried from the vicinity of the kilns. Before commercial quarrying started, almost every farmer located within the limestone region had their own kiln to manufacture lime.
York Township
Iron mining in York County was one of the leading industries in the 19th century. Over 170 mines operated in the county, removing both limonite and magnetite. Careful examination while driving the roads can often detect remnants of these mines. Pictured here is the waste pile of the Moser’s (new) bank near Ore Valley, just east of Dallastown. This beautiful stone house has a perfect setting along Springwood Road. In the back yard, a large pond is found today which was the excavation of the open pit mine, then often, referred to as “banks.”