by the members of CPSP118G Group III.
Alejandro de los Reyes
Sideling Hill Interpretive Center
The Sideling Hill Road Cut
The Oriskany Formation
The Keyser Formation
How to Measure Strike and Dip
Along Interstate 68 in western Maryland lies the premiere geological
outcrop in the northeastern United States, the Sideling Hill road cut.
Next to this outcrop is the Sideling Hill Interpretive Center which provides
a scenic view overlooking the Appalachian Mountain system. The Interpretive
Center consists of two levels, both providing visitors with information
about Sideling Hill.
On the ground level, there are employees equipped with maps and brochures to aid visitors. Not only are they knowledgeable of the best restaurants and hotels in the area, but they also know a bit about the geology of the region as well. The second level provided a geological background of the region, with exhibits that illustrated the diamond headed drills used during construction of the road cut. Samples of metamorphic, sedimentary, and igneous rocks were also available to allow hands-on learning. A small-scale model of the Sideling Hill outcrop and its surrounding region was on display for visually impaired visitors.
On the lower level, the Earth Life & Time group was addressed by Dr. Kenneth Schwarz, a geologist with the National Geological Survey, and Mr. Wally deWitt, a former employee of the federal government who is now retired. Following a brief introduction by Dr. Schwarz, Mr. deWitt gave a slide show presentation.
The slide show presentation provided us with a brief overview of the
construction, geology, and history of the Sideling Hill outcrop. We were
told that in April of 1983, Hallway Construction Company began drilling
and blasting. In August of 1984, 5 million pounds of explosives were used
to take out 10 million tons of rock. Finally in mid-summer of 1985, the
road cut was finished, standing 350 feet high. However, it was not until
August 2, 1991 that the exhibit center was opened and dedicated to Marylanders
who served in the Vietnam War. A speech was given by the former governor
of Maryland at the dedication. A short time later, the bridge crossing
the interstate was dedicated to the representative responsible for obtaining
funds for construction of the interpretive center.
In addition, the slide show provided us with a geological background of the region. We learned that Sideling Hill is 80 miles long. It is actually one of the smaller areas of the Appalachian Mountain system. There is a section along the road cut, 60 feet in length, where a natural gas line is located. The gas line runs all the way down the eastern side of the US to the Gulf of Mexico.
While observing the hill, we were able to see how some of the
geologic terms we learned, such as anticlines and synclines,
applied to the area. Sideling Hill is a syncline, or a fold in which
the strata on either side dip down and inward toward the axis. The downwarps
were worn away by erosion and swept eastward. Layers of rock in the road
cut were also introduced. The dark zones in the Rockwell formation of the
cross section were once a fossilized swamp. There is also a fault generated
by the pressures that bent the rock. There were sandstones found within
the rocks, which are porous and permeable. During the spring, summer, and
fall, water precipitates out of the fractures in the rock along the axis.
Finally, a short summary of the history was given. Compressional stresses developed on the earth's crust by the collision of the North American and African continents during the late Permian and early Triassic (230-240 million years ago). The Rockwell and Purslane Formations were deposited during the early Mississippian (330-345 years ago).
Overall, the Sideling Hill Interpretive Center is both a fun and educational
place for geology students like ourselves, as well as the general public.
By Nick Condrey
Images obtained by Eric Samson
November 30, 1999
Dr. Schwarz and Mr. Dale Shelton led small groups of students
out onto the outcrop itself. To visit the outcrop, we walked out onto of
one of the twenty-feet wide benches or "berms" that prevent falling rocks
from reaching the road and allow researchers to examine the rock closely.
We all received hard hats to ensure our safety and the journey along Sideling
The outcrop consisted of several
different types of sedimentary rock types:
- siltstone: clastic sedimentary rock containing silt-sized particles
- sandstone: medium-grained clastic sedimentary rock
- shale: fine-grained clastic sedimentary rock, containing clay and silt particles
- coal: peat swamps compressed over time produced coal
- diamictite: one of the lowest strata in the hill; poorly sorted to unsorted rock containing clay, silt, sand, and pebbles.
As these rocks were deposited, the shore of a shallow sea had moved back and forth across the site. Some of the sediments that were to form the rocks were deposited in shallow marine water, but most were deposited in floodplains near the ancient shore. The presence of coal revealed that a swamp region on the flood plains at one time. In the image to the left, a block of coal from a higher layer has fallen onto the berm. The origin of the diamictite is still questionable, as no accepted theory has been suggested.
Several examples of physical erosion were identifiable along the outcrop.
Winds up to one hundred miles per hour hit the face of the rock at times
causing this erosion. pencil shale: thin, pencil-shaped rocks consisting
primarily of shale.
Aquifers were present throughout the permeable sandstone layers. Characteristics of these include:
Cross bedding was seen in many
the sedimentary rock layers. Currents of water in the ancient streams in
which the sediments were deposited resulted in small beds inclined with
respect to a thicker stratum within which they occur.
Within parts of the outcrop, we
were able to see examples of soft-sediment deformation. Such deformation
frequently occurs when thick layers of sand are quickly deposited over
soft mud. As the sand settles on top of the mud, it creates more and more
pressure, forcing water from the mud. This allows blobs of sand to sink
into the mud layer on which they have been deposited. Several million years
from now, the sand deposited by hurricane Floyd at Two Run Creek will resemble
the blobby sand layers at Sideling Hill..
Fossils found along the outcrop consist primarily of plant fragments. Although we did not find any animal fossils ourselves, we can take the word of the expert on the fact that they have been found before. These include several marine fossil types, including of brachiopods and bivalves.
The outcrop was cut by several fault planes. Slickensides revealed the
direction of movement along the fault plane. Running ones fingers along
the plane in the direction of movement, the slickensides surface felt smooth.
Running the fingers opposite this direction caused a rough sensation.
Images obtained by Christopher Wordlaw
November 30, 1999
After our visit to Sideling Hill, we drove a few miles east to
the Sandy Mile area, a place more rural, and not as developed as Sideling
Hill. There, we were able to see parts of the Oriskany Sandstone, a formation
from which the Sandy Mile got its name. We also observed the Keyser Limestone,
which was a only short distance from the Oriskany formation. We were able
to advance our knowledge of geology while taking time to observe and study
these two areas.
The Oriskany Sandstone formation
is found in the Lower Appalachian plateau. It is believed to have formed
during the Devonian period (345-405 million years ago) in a beach or shoreline
environment. The Oriskany group is composed of siliceous rocks, which are
mainly quartzose sandstone. The specific formation that we visited lies
next to Sandy Mile Beach.
The Maryland Oriskany stratum is primarily
made up of Ridgeley sandstone. Ridgeley is pure quartz sandstone, usually
of a light gray color. This finely grained sandstone ranges from 100-400
feet thick throughout Maryland. The sandstone contained vast numbers of
animal fossils, but the most commonly found were brachiopods and gastropods.
These fossils were easy to find, as they were usually preserved as molds
in the sand.
By Gianna Alvino
Images obtained by Ryan McCullough
November 30, 1999
The Keyser Limestone formation is found in the Appalachian Mountains and although the exact date of formation is still questionable, it is believed to have formed during the Silurian period (405-425 million years ago). The formation consists of shaly fine-grained limestone, which is about 270 to 290 feet thick and contains many animals. Essentially, the entire formation is biogenic hence everything is technically a fossil that is found there. The formation lies next to the Sandy Mile Beach. The sand is younger than the limestone, but is one the side, only due to the fact that when the Appalachian Mountains were formed, folding occurred, displacing the sandstone.
The fossils that were found there were ostracodes, brachiopods, crinoids,
and bi-valve crustaceans. While looking through the limestone formation,
one was able to find many examples of each of the different types of fossils,
and later on able to identify many of them.
The ostracodes were the most common.
They are bi-valve filter feeding crustaceans which were basically similar
to tiny shrimp. They lived in the water and breathe through gills; they
have a hard outer shell, and jointed appendages. The ostracode tended to
be more abundant due to its smallness: the average one was about 3 to 4
millimeters in length.
The next group of fossils found was the brachiopods. These were basically two shelled animals, which contained upper and lower valves. Although brachiopods and bivalve mollusks, like clams both have two shells or "valves", their geometry is fundamentally different. When clam shells close, they meet at the animals bilateral symmetry. The valves of brachiopods, in contrast, come together in a plane perpendicular to that of bilateral symmetry. These were filter feeders just as the ostracodes, although they were not as common. The shells on them were made of calcium carbonate, which is the main component of limestone; therefore, they made up part of the formation itself. With the brachiopods, more than one species was identified, which were: Chonetes jerseyenis, and Meristina praenuntia. These two species could be distinguished with a hand lens.
The next fossils that were obtained were the crinoids, or more commonly known as sea lilies. The name is misleading though in that these were not plants, but animals that belong to the Echinodermata, and were relatives of the starfish. They were immobile creatures, which had stalks that rooted them to the ground. These stalks were made up of stacks of round disks, which are the remnant fossil that will be found in the formation. These disks, named columnals each had a hole down the center where the tissue was contained. The hole would either be circular, or a have a pentagon shape to it. The reason that it would have a pentagonal shape would be due to its five-fold symmetry. On top of the stalk was a mouth with tentacles with which it would be able to catch its food with and eat.
The last fossil type that was found would be the bivalve mollusks. The
size of these can range anywhere from the size of a pin head to giant which
is in excess of two meters. During the Silurian time, though, the size
was typically smaller, ranging from about 2 to 10 centimeters. Normally.
As inferred from the name, the bi-valves consisted of two halves, which
were similar to one another. The genus that is found most commonly here
is Mytilarca. There are many different ones, which may be found throughout
the formation, due to how common they were at the time of preservation
of the fossils.
Strike and Dip
Images captured by Justin Fry
November 12, 1999
Strike and dip are two words used by geologists to specify the orientation of a plane in space. The strike tells the direction of the line made by the intersection of the plane being described with the horizontal plane. It is a compass direction and is so given relative to north. It should be noted that although a compass points to magnetic north, the compass used to measure strike and dip, called a Brunton Compass, is calibrated to account for local declination and thus gives an angle relative to geographic north. The dip tells about how steeply the plane is angled. Its value is the maximal angle between the plane and the horizontal. The dip line is always perpendicular to the strike line. The outward face of the plane will usually face more toward north or south, and this specification is also attached to the dip.
As an example, if a flat rectangular object were oriented with its long axis pointing east - west, then tipped up to a forty-five degree angle so that its top was facing north, its strike would be ninety degrees and its dip would be forty-five degrees north.
|Strike and dip are measured as follows:
1. Strike - The compass is placed with an edge touching the plane,
|2. Reading strike - The compass is placed with the face of an edge on the plane, then held horizontal by centering the circular bubble balance as shown in the picture below. The orientation of the arrow in the compass is then the strike. In this illustration, the north arrow is not visible, but it points 180 degrees from the south arrow - 266 degrees. This is the strike.|
|3. Dip - The compass is placed with the face of an edge on the plane||
4. Reading dip - The clinometer in the compass casing is adjusted with a lever on the bottom of the compass until the bar bubble balance is centered, indicating that it is horizontal. The angle the clinometer then points to is the dip. In this case, it is 27 degrees south,