Silver Comet Trail - Geology

Geology

By riding or walking the Silver Comet Trail, it is immediately obvious that construction of the original Silver Comet Railroad line involved levelling out most of the hills and valleys over which the rails were made to traverse. Most interestingly, where hills were encountered, "road cut" techniques were employed to ensure that the railroad bed was graded as flatly, as possible. The road cuts now reveal many interesting rock formations along the edges of the Silver Comet Trail's pavement. Many of the formations include quite steeply dipping (tilted) layers of metamorphic rocks (presumably associated with one or more episodes of mountain-building that produced the Appalachian Mountains, and related physiographic provinces, in Georgia).

In Paulding County, the Silver Comet Trail crosses over the Allatoona Fault in at least three places, and where the trail intersects the fault in the vicinity of Willow Springs Road (currently identifiable as a long wooden automobile bridge high above the trail), the fault serves to divide the quite distinctive Eastern Blue Ridge rocks from those that most characterize the Western Blue Ridge Province.

One rock formation of particular note along the Silver Comet Trail in Paulding County is the Ordovician-age Pumpkinvine Creek Formation (PCF). The PCF is primarily composed of metamorphosed volcanic rocks thought to have originated out in the now-vanished, ancient ocean geologists generally refer to as Iapetus.

Per theory, the PCF, and other such volcanics, formed in the Iapetus as sea-floor rocks (and, perhaps, even entire volcanic islands), but were ultimately rammed up out of the water by colliding continental masses that finally obliterated the ocean, itself. These volcanic rocks were accreted, well inland, onto what eventually became our modern North American continent.

The meta-volcanic rocks of the PCF are believed to be the remnants of the sort of exotic "accreted terranes" described above, and exposures of PCF rocks can be found on the Silver Comet Trail near the Allatoona Fault.

A detailed geologic map of the area in Paulding County was completed by Christopher S. Holm, Ph.D., and can be viewed at http://etd.lib.fsu.edu/theses/available/etd-11132006-173338/unrestricted/yorkvilleGA.pdf. The map clearly shows the Silver Comet Trail, the Allatoona Fault, and the various rock types a hiker or cyclist will encounter in the above-mentioned section of Paulding County, Georgia.