Blue Ridge Geology Field Trip

The photographs below were taken on a joint class trip of structural geology and petrology students. The Blue Ridge province contains the highest mountain peaks in Virginia and is underlain by the oldest rock units exposed within the Commonwealth. The field trip begins along exposures and trails found on Skyline Drive within Shenandoah National Park. Most of the massive igneous rocks that underlie the Park are comprised of granitic rocks that formed during the mid-Proterozoic as a result of the Grenville Orogeny.

The tunnel shown in the picture below, was cut through granite rock just south of the Thornton Gap entrance to Skyline Drive. The darker rock unit, to the right of the tunnel entrance, is a diabase dike that has cut-through the older, lighter color, granite seen on the far right. Characteristic cooling joints can be seen within the diabase. The diabase dates to the latest Proterozoic and beginning of the Cambrian and is interpreted to represent a feeder dike created when rifting of the continental margin began.

The photograph below was taken along Stony Man Trail which begins along Skyline Drive and continues to higher elevations to the south of the parkway. Along the trail eroded remnants of diabase sills or lava flows may be seen complete with columnar cooling joints.

The view from the top of Stony Man Trail overlooks the Shenandoah Valley and the characteristic parallel peaks of the Valley and Ridge province of Virginia. Most of the valley floors are underlain by soft shales or soluble carbonate rocks, while the higher peaks contain sandstones or quartzite which are more resistant to erosion.

Along the upper portions of Stony Man Trail, students can find former lava flows that occurred in the late Proterozoic and lower Cambrian. Evidence of approximately 18 separate lava flows may be found, separated by intervals of sedimentation. The upper surfaces of the now cooled lavas is marked by well preserved vesicles. These are the holes left by escaping gases as the lava is still cooling and crystallizing.