Egg-cellent Rock Collection Activity!

A light brown fossil on pale tan stone.

NPS Photo / Fossil Butte National Monument, Lincoln County, Wyoming

Why are rocks important?

Rocks contain clues about what Earth was like in the past! Scientists that study rocks are geologists. Geologists use the science of geoscience to study and learn about our planet and events that happened long ago by studying rocks all around us. This research helps with natural resource management. To learn more about geoscience and other different types of geoscientists, visit our Junior Geoscientist page.

 

Construction lasted about 22 years along the canal.

NPS Drawing

Geography along the C&O Canal:

From the very beginning of the Chesapeake and Ohio Canal, geography would prove to be a challenge. On July 4, 1828, United States President John Quincy Adams worked up a sweat as he attempted to “break ground” during a ceremony to start construction of the C&O Canal. Time after time his shovel hit rock just below the ground’s surface. President Adams didn’t give up though, and after several attempts he finally scooped the first shovel of dirt – the crowd watching cheered! And then, the real work began. The ominous ground-breaking ceremony foreshadowed the challenge awaiting canal workers, as they worked to build a canal for hundreds of miles in rocky terrain along the Potomac River and into the mountains.

“Sandstones, limestones, dolomites, metamorphic and igneous rocks were quarried along the river for the construction of the canal” (Thornberry-Ehrlich, T. 2005).⁵ Today, C&O Canal park geologists have identified a variety of rocks in the park. Geologists use a wide variety of terms in their field of work. Learn some of the definition’s geologists use and view the gallery of rocks found along the C&O Canal below:

 

Definitions & Phonteic Spelling

Inhabitant (In-hab-i-tant): A person or animal that lives in a particular area or place.

Conglomerate (Con-glom-er-ate): Geology-Rock made from a mixture or fragments of several sources.

Fragment (Frag-ment): a broken piece of something, in this case broken rock.

Calcium carbonate (Cal-ci-um carb-on-ate): A white solid substance that occurs naturally in bones, shells, limestone, and chalk.

Bluff (Bl-uff [uph]): A type of broad, rounded cliff which usually boarders a river, beach, or coastal area.

Bitumen (Bi-tu-men): Natural tar created by the breakdown of organic material such as wood or plant matter. Often used throughout history as a sealant on roofs, boats, and roads. Bituminous coal contains a small amount of bitumen.

Tributary (Trib-u-tary): A stream that flows into a larger stream or body of water such as a lake.

Invertebrate (In-ver-te-brate): An animal who lacks a spinal column (spine) [Ex. Insects, octopus, jellyfish, snails, or corals].

Excavation (Ex-ca-va-tion): The act of digging out or through something solid. In this case it was the Alleghany Mountain to create the Paw Paw Tunnel.

Aqueduct (Aq-ue-duct): An artificial waterway structured like a bridge to allow water and small boats to pass over a larger stream or river.

Weathering (Weath-er-ing): the effect of weather conditions changing the physical appearance or texture of an object such as rocks.

Manufacture (Man-u-fac-ture); Manufacturing (Man-u-fac-tur-ing): The process of creating and making products (I.e. food, toys or in this case glassware) to sell. Products are usually made by using raw materials and either by hand or machine.

Erosion (Ero-sion): The removal of soil, rock, or dissolved material from surface location by wind or water flow. This can happen in one quick event such as a storm or gradually over time.

Adaptation (Ad-ap-ta-tion): The process where an organism develops and changes over time to survive in its environment.

Observation (Ob-ser-va-tion): The act of inspecting something and taking note of what you discover.

Data collection (Da-ta Col-lec-tion): The process of gathering information based on facts that can be calculated and discussed with reason.

Classification (Clas-si-fi-ca-tion): The process of grouping together information based on a certain standard (I.e. Category).

Sort (S-OR-t): A method of organizing items.

Igneous (Ig-ne-ous): When hot, molten rock (magma) hardens, usually after volcanic activity. To learn more, visit Igneous Rocks.

Sedimentary (Sed-i-men-ta-ry): Pieces of pre-existing rock or once-living organisms get crushed and buried, forming this new type of rock. To learn more, visit Sedimentary Rocks.

Metamorphic (Meta-mor-phic): The process of changing form. In this case, rocks, are stretched, twisted, and folded as they cool. To learn more, visit Metamorphic Rocks.

 

The C&O Canal’s Rock Collection:

 

Spear Points similar to the ones created by the first inhabitants (hunters & gatherers) of the Upper Potomac River.

NPS Photo / Kelly Savannah

Spear Points (Arrowheads)

The first inhabitants of the upper Potomac River were hunters and gatherers and they would make their spears from volcanic stone called rhyolite, which can be found on certain slopes of the Blue Ridge and Catoctin Mountains. Spear points were most likely made between 7800 and 6000 BC and would often have a split or “bifurcated” base (Bedell, J., Fiedel, S., & Shellenhamer, J., 2011).¹

 

Balls Bluff Siltstone (Leesburg Member)

NPS Photo / Kelly Savannah

Siltstone (Leesburg Member)

This is a limestone conglomerate (mixture) composed of limestone and other rock fragments from previously existing rock formations cemented together by calcium carbonate (Ex. what chalk is made from). The reddish color is due to the iron content in the silt. Fragments of this rock are sub-angular in shape and vary in size. The name Balls Bluff, originated from being quarried on both sides of the Potomac River Valley near Washington, D.C. Interesting fact: It is also known as Potomac marble by builders due it’s multi-colored appearance, although it is not marble and the columns of the United States Capitol are made of this stone (USGS, 1999).⁶

 

Bituminous Coal

NPS Photo / Kelly Savannah

Coal

Known as "the rock that burns clean," high quality coal is formed from decaying plant matter. Bituminous coal can be found near the canal’s terminus at Cumberland, Maryland. This was a valuable resource for factories, warming homes, and transportation, based on its relatively clean burning in the 19th and 20th centuries. To learn more visit Cumberland Coal.

 

Conococheague Limestone

NPS Photo / Kelly Savannah

Limestone

Conococheague Limestone is an impure limestone containing layers of silt and dolomite (a solid form of organic materials). Unlike most limestone, it is hard and resistant to erosion. It has been used as a building stone in the Williamsport, Maryland area, and in the construction of the C&O Canal aqueduct over Conococheague Creek; to which it was named.

 

Top of the image is a Mahantango Formation and on the bottom of the image is of "Pencil Cleavage"-Uneven shards of rock that has broken off that resemble pencils.

Top Image: NPS Photo / Kelly Savannah; Bottom Image: NPS Photo / Nanette Nyce.

Shale

Mahantango is a sedimentary rock that is predominantly made of shale and although it is solid, it is known to fracture. This type of shale commonly contains fossils of small marine invertebrates, known as brachiopods. Most brachiopods like mollusks or clams use their pedicle (fleshy arm or limb), to move up and down within mud. It has been hypothesized that these small creatures dug through the mud before it hardened resulting in the fossils that we see today. During C&O Canal excavations, the rock would break into long, slender, and uneven shards as shown in the picture to the left. This made excavations (digging) in an abandoned valley of Mill Run at Oldtown easier for construction because there are bluffs of shale along the Potomac River that prevented construction of a canal and towpath (Southworth et al., 2008).⁴

 

Manassas Sandstone, aka Seneca Red Sandstone. The rock in the top of the image has a gray, deep purplish brown color whereas the rock on the bottom of the image has a red tone to it due to the iron oxide that changes the stone’s color to a rust red.

NPS Photo / Kelly Savannah

Red Sandstone

This fine-coarse grained sandstone contains tiny flakes of mica and may locally contain small pebbles. Named for exposures near Poolesville, Maryland this sandstone is called Manassas Sandstone by geologists and is also referred to as, Seneca Red Sandstone for the iron oxide that gives the stone’s its rust red color and that it has also been found near the mouth of Seneca Creek, in Seneca, Montgomery County, Maryland. (Lee, K.Y., and Froelich, A.J., 1989). ² The colors of the stone range from a gray, deep purplish brown to red as it is weathered. This stone was a favorite building stone and was transported to Washington for several building sites along the canal such as lock keepers’ houses, the Seneca Creek Aqueduct and even the Smithsonian Castle on the National Mall in Washington, D.C.

 

Oriskany Sandstone; A white quartz sandstone

NPS Photo / Kelly Savannah

White Sandstone

This pure white quartz sandstone is soft and can easily crumble when exposed to weathering. This is because the cement that holds the quartz grains together is predominately calcium carbonate (Ex. what chalk is made from). Oriskany Sandstone was not widely used in the construction of the canal based on its tendency for weathering. However, its natural gas bearing formation made it widely popular as a source of silica for manufacturing the finest of crystal glass products.

 

Paw Paw Tunnel and Towpath

NPS Photo / Ranger Hollie Lynch

Construction verse Nature

Construction of the canal was a tough and hard task for the canal workers. The rough terrain and mountain took a lot of time, money, and energy. In fact, the original plan was to build the canal all the way to the Ohio River in Pennsylvania so that boats could travel to the West. However, by the time, the canal company reached Cumberland, Maryland, and the experience of the Paw Paw tunnel (Digging a 3,118-foot tunnel through the hard, loose shale), the decision to continue through the Allegheny Mountains to Pittsburgh, Ohio, was no longer an option. Even, though the company never made it to Ohio, they kept the name, which is why the canal was named C for the Chesapeake Bay and O for the Ohio River! (See image of proposed map route below). Visit, Canal Construction for more information.

 

A map of the proposed route of the C&O Canal.

NPS Map

Click on the map to the left to view a larger image!

 

2016 Shale Rockfall

NPS Photo / Ranger Hollie Lynch

Rockfalls at the Paw Paw Tunnel

In 2016, there was a major rockslide that occurred at the north portal (downstream entrance to the tunnel) of the Paw Paw Tunnel; Refer to the image to the right. Rockslides (rockfalls) are natural geological processes that take place when rock breaks and moves freely from a cliff face downward at fast speeds. There are many causes for rockfalls such as, earthquakes, water, and vegetation (plant) growth. Earthquakes occur when the earth’s plates shift and collide, causing the earth to shake and rocks to tumble down (rockslide). This is rare to our area but can happen. If water enters through cracks in rock formations then freezes and thaws; process called "frost wedging" or "freeze-thaw," this can cause the rock to loosen and fall away from the cliff. Additionally, plant growth such as firs, pines and other evergreen trees grow in rocks; when their roots expand, they can break through the rock causing rockfalls to occur (Rockfall, 2021).³

 

During the 2017-2019 project work, the rock wall along the towpath was bolted and pinned with rockfall mesh to prevent future rockslides.

NPS Photo / Joe Reed, Park Engineer

The 2016 rockslide at Paw Paw tunnel left large pieces of loose shale, which presented a safety hazard to visitors and the boardwalk section of the towpath. This prompted the 2017 project to stabilize the slope, which was completed two years later in 2019; Refer to the image to the right. In 2020, the park planned a new project to remove the remaining rock that had fallen in 2016. Once permits have been finalized, the project should officially begin in 2021 and finish in 2022. To learn more about the project, visit Paw Paw Tunnel Scaling Project.

 

Illustration of an egg carton with rocks inside, a paint palette and paintbrush.

NPS Image / Kelly Savannah

 

A collection of rocks set inside an egg carton with a magnifying glass next to the egg carton.

NPS Image / Kelly Savannah

Egg Carton Rock Collection Activity!

Looking for a fun and educational activity for learning about rocks and minerals? Be a geologist for a day, get outdoors, and explore! Use your supreme observation skills to learn about the geology around you. Try creating an Egg Carton Rock Collection.

 

Resources

1 Bedell, J., Fiedel, S., & Shellenhamer, J. (2011). A PATH THROUGH THE MOUNTAINS: THE ARCHEOLOGY AND HISTORY OF THE CHESAPEAKE & OHIO CANAL NATIONAL HISTORICAL PARK. The Louis Berger Group, Inc. Handbook for The National Park Service National Capital Region, pg. 9.

2 Lee, K.Y., and Froelich, A.J., 1989, Triassic-Jurassic stratigraphy of the Culpeper and Barboursville basins, Virginia and Maryland: U.S. Geological Survey Professional Paper, 1472, 52 p.

3 Rockfall. (2021, January 12). National Park Service, Yosemite National Park, California. https://www.nps.gov/yose/learn/nature/rockfall.htm

4 Southworth, Scott, Brezinski, D.K., Orndorff, R.C., Repetski, J.E., Denenny, D.M., 2008, Geology of the Chesapeake and Ohio Canal National Historical Park and Potomac River Corridor, District of Columbia, Maryland, West Virginia, and Virginia: U.S. Geological Survey Professional Paper 1691, 144 p., 1 pl. (Also available online at https://pubs.usgs.gov/pp/1691/.)

5 Thornberry-Ehrlich, T. (2005). Antietam National Battlefield, Chesapeake and Ohio Canal National Historical Park, & Harpers Ferry National Historical Park, Geologic Resource Evaluation Report. Natural Resource Report NPS/NRPC/GRD/NRR—2005/006. National Park Service, Denver, Colorado.

6 USGS. (1999, January 13). Stone 3. Publications Services. https://pubs.usgs.gov/stones/stones3.html