One of the most photographed sites along the C&O Canal is the The Devils
Eyebrow. Located along the towpath at mile 127.25, adjacent to
the ruins of The Round Top Cement Company, the eyebrow is a
beautiful and massive fold in the rock strata, and the subject of
this Appalachian Tale.
Circa 1897
The Appalachian Mountains are ancient. When the earth was younger,
about 480 million years ago, this area was covered by a shallow
sea. Thick layers of sediment and carbon rock were deposited on the
sea floor. Over the millennia, and due to alternating actions of
climate change, receding seas, erosion and the shifting of large
segments (tectonic plates) of the earth’s crust, the
Appalachians were born. During the violent collisions of these
moving plates, one plate would wedge itself under the other causing
massive upheavals and folding of the earth across great distances.
This wedging action is known as subduction.
At The Devil’s Eyebrow, this up-thrusting and folding of
ancient rock strata resulted in what is called an anticline.
The devil’s furrowed eyebrow, and the huge hollow area
within, were formed by this folding action combined with erosion of
the soft, calcium-rich lower layers, leaving the harder and
resistant strata above in tact.
Anticline
Most of these visible formations are the direct result of human
presence and progress - building of the canal and railroad, as well
as mining operations. Several reknowned geologist have stated as
much. Ernst Cloos, of Johns Hopkins termed the Round Top exposure
as a veritable laboratory of the mechanics of folding, formation
of cleavage, thrusting, and the deformation of bedded rock.
Peter Geiser concurred that ...much of the value of the section
lies in the fact that deformation at this locality has progressed
only far enough to show early structures, but not to the point of
obliterating sedimentary features.
The mining side of this 'laboratory' features the foundation and
kilns of the once-thriving Round Top Cement Company. In 1837,
during construction of the C&O canal, A.B. McFarland recognized
the quality of the calcium-rich limestone within the anticlinal
folds, and its’ commercial value for the manufacture of
cement.
The Round
Top Cement Company was in operation from 1837 until the early
1900’s. Limestone was mined from seven primary openings, the
largest having 500 feet of passage, and being 20 to 50 feet high.
The majority of these mines are straight passages which follow the
path of the anticlinal folds. Evidently the rock was easily mined
by ‘peeling’ the soft rock strata off the walls as
slabs. Consequently, most of the mines here have triangular
cross-sections similar to that of The Devil’s Eyebrow.
Three of the mine openings are visible from the nearby (directly
above) Western
Maryland Rail Trail. The openings are gated to protect the bat
colonies within.
Access to this site is by bicycle or on foot. Parking for
towpath and rail trail access is available in Hancock drownstream,
and from Willow Road upstream. Parking coordinates are posted on
this page.
The listed coordinates are for two National Park Service
interpretive signs. Both expand in detail the physical and natural
history of The Eyebrow and adjacent Cement Mill. From the signs you
will be able to garner information needed to answer three of the
following questions. The fourth will require the knowledge of what
you have learned and your observational skills. No photos are
required, but feel free to upload the memories of your visit.
E-mail the cache owner with the answers for the following
Tasks.
Task#1 – The rocks here tell a story of a violent
collision. Please explain.
Task#2 – Beside rising competition in the cement industry
and the advent of rail frieght, what event caused the Mill to cease
operations?
Task#3 – What are some of the uses of limestone, and how
many tons of burnt lime were produced at Round Top Cement in a
day?
Task#4 – Take visual note of the row of kilns between the
Mill foundation and the Eyebrow. What type of geological formation
are they built upon?
Gratitude is in order for the Rangers and Resource Staff at
C&O Park Headquarters for their patient and timely assistance
in bringing this Earthcache to fruition. At a time when
governmental funds are dwindling, Park official requested help with
removal of trees and underbrush to better expose the view of The
Devils Eyebrow. Special thanks is also in order for the crew who
toiled and sweated on-site to provide an unfettered view of this
unique place -julia51, trainbug, Manitto, LpYankeefan, &
Md8baller.
FTF - CCrew -
Congratulations