BLOOMSBURG FORMATION

WILLS CREEK FORMATION

                  TONOLOWAY LIMESTONE                                        

Site Location: 

Round Top Cement Mill, Mileage:  

127.24 to 127.40

      (Nearest Access: Canal (Berm) Road, mileage 125.60)

  This site features the foundation remains and kilns of the once thriving Round Top Cement Plant as well as one of the most often photographed sites along the Canal, Devil’s Eyebrow.  Devil’s Eyebrow is an especially symmetrical anticline (flexure) that plunges to the north.  Its charm comes from the natural hollowing out of the less resistant calcium-rich rock to form a shallow cave.  Devil’s Eyebrow has an educational history in that its photograph appeared in early geology textbooks.  Actually small folds of this sort are common in the surrounding area; in fact, another can be observed directly under the row of kilns  >

The cement plant was a vital part of Canal construction because limestone of the quality required for making cement was practically nonexistent between here and Cumberland, a distance of about 57 miles.  Limestone, especially from the very pure Tonoloway, was mined along the berm upstream of the plant, transported to the kilns, calcined, and the product transported to the adjoining plant.  The Tonoloway was mined, not quarried; drift adits are to be found along the old railroad bed above the Canal.  The State of Maryland has closed off the mines with heavy gates as a safety precaution prior to paving the railroad bed as part of its Rails to Trails program and to protect certain indigenous species that reside in them.  A segment of that paved trail now exists east of Hancock and is expected to extend many miles to the west.  Access to the segment above the Round Top is from the Loner siding lane opposite the Locher House.

  The rock formations exposed here are described as red shale (siltstone) and sandstone of the Bloomsburg overlain by shale and limestone of the Wills Creek and Tonoloway.  It is believed that the upper portion of the red shales and sandstones of the McKenzie Formation are also present here, at and below the level of the towpath.  This sequence is interpreted as a cyclically transgressive/regressive (thus, laterally fluctuating) shoreline that periodically provided an environment in which iron was deposited in its oxidized, red, form.  With time the basin deepened and received carbonate precipitates.  The Wills Creek marks the transition from clastics to precipitates such that by Tonoloway time only carbonates, essentially devoid of silt or sand, were deposited.  

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