Thursday, February 12, 2015

Geology of Rockingham

Rocks of Rockingham

                 Without being too technical, this article focuses on the geology and geography of Rockingham County with specific detail on natural features found in the western portion of the County.  We hope you will be encouraged to take a new look at your neighborhood.  History, economy, recreational activities, and even governmental decisions are profoundly affected by our landscape.
                We know that Rockingham County was named to honor the Marquis of Rockingham, Charles Watson-Wentworth, who opposed the suppression of the American colonies.  However, anyone who has put a spade in the soil around here knows the “rock” in Rockingham for another reason.   We pity the early settlers who had to move boulders and rocks to build the County and its roads.  In the early history of byways in the County, the policy on infrastructure upkeep was that residents along a road were responsible for getting out their sledge hammers to break-up the stones to keep the roads repaired![i]
Rocks present obstacles and define activities, but one should take a moment to look closely at the rocks.  In this place, in one hand you can hold a small rock that is more than 300 million years old.  In the other hand you can hold a pen that has been recording the history of the area for only about 300 years.  Three hundred million years ago, in the Paleozoic Era fishes were evolving as were land plants, and more important for the stratigraphy and structural features of our landscape, it was the era of sandstone and coal deposits and the folding of the Appalachian Mountains.  (The evolution of dinosaurs and their extinction was a couple of millions years in the future.)  Three hundred years ago Governor Alexander Spotswood and his party of explorers crossed the Blue Ridge Mountains and viewed the Shenandoah Valley.  In an account of this first crossing a member of this exploration remarked that Spotswood “could not grave anything” to mark their arrival because the “stones were so hard.”  Another member of the expedition noted that the party was provided with “horseshoes (things seldom used in the lower parts of the country, where there are few stones).” [ii]

 In this time span of more than three million years, and even before, geological events shaped the landscape.  The results of these events provided much of the economic basis for activity in the area, which included mining, water and distillery bottling, pottery, and hospitality.  Rock outcroppings, mountain clines, and water courses defined boundaries and provide recreational activity.  The geological formations provided the source for legends and for artistic imagination and endeavors, as well as scientific curiosity.  Fortunately human intrusion has been mostly respectful of the natural environment.  Humans have been content, if at times inconvenienced, to leave changes to natural forces.
Some 400 to 300 million years ago during the Devonian, Mississippian, and Pennsylvanian periods in the Paleozoic Era, sandstone was deposited by meandering rivers in the Shenandoah region.  Sandstone is cemented sand containing predominantly quartz and is the most abundant, durable mineral on the earth’s surface.  Sandstone color variations can be attributed to the mineral content, degrees of oxidation, ferrous content, and shale.  The following illustration is the stratigraphic scheme of the ground beneath our feet from Little North Mountain to the top of Shenandoah Mountain. 
The next time you pick-up a sandstone rock, note the colors and then imagine the land upheavals that brought this particular rock to the surface for you to hold in your hand.  Also contemplate how far below your feet is a lot more of this sandstone.  Without having to dig, you can drive west on Route 33 toward the West Virginia border and see in the road cuts the two top formations: Pocono and Hampshire.
The accompanying table explains the map symbols and the character of the layers.  Mostly the focus is on Devonian division in Paleozoic Era.
Notes on Western Rockingham County Geology

From the Paleozoic Era



in feet


Appalachian Mtn Fold



Coal and Sandstone

Pocono formation
Massive white-grey sandstone with

some dark shale

Upper Devonian Period - Sandstone and Shale

Hampshire Formation
Chiefly red sandstone, some flag-

stone, shales, and mudrock

Chemung formation
Grey to greensih silty sandstone and

brown to grey shale, fossiliferous

Brallier Shale
Greenish brown stiff micaceous

shale and fine grained thin bedded

 greenish sandstone

Source: William B. Brent.  Geology and Mineral Resources of Rockingham County.  1960.  p.10

               Keith Frye.  Roadside Geology of Virginia.1986. p.8

Structural Features
Geologists assume that the structural faults and folds took place during the building of the Appalachian Mountains near the end of the Paleozoic Era.  In western Rockingham County are two of the County’s four northeast-trending fault areas.  The first fault, noted on the stratigraphic map, is the Little North Mountain Fault.  The Little North Mountain Fault zone extends 27 miles in a northeast and southwest direction across the County. The Fault crosses US Route 33 about 2.5 miles west of Hinton.  The second fault structure area is between Little North Mountain and the Shenandoah Mountain crest at the western boundary of Rockingham County. 
In the area of Rawley Springs and in the area west of it are two structural folds.  These major folds also cross Rockingham County southwest to northeast.  The first fold is the overturned and southeast dipping West Mountain syncline which forms the prominent ridge of Narrow Back Mountain and which forms the southeastern boundary of the former Rawley Springs resort area.  The overturning was a result of the drag from movements along the Little North Mountain Fault where there Little North Mountain is absent. [iii]
The second northeast-trending folding structure, farther to the west and barely crossing the Riven Rock Mountain, is the Bergton-Crab Run anticline.  Here the rocks are sloping downward in opposite directions on both sides of the mountain.  The fold axis roughly parallels the axis of the West Mountain syncline.  Relating these structures to the strata, the age of the rocks in the faults is of Devonian and the age of rocks involved in the folding is Mississippian. [iv]
Seeing the Geological Features
Since the 1800’s, the rock formations named Juliet’s Tower and Lovers’ Leap along the Rawley Aretes have made the Rawley Springs a favorite for rock scramblers.  Other intimate and challenging encounters with rocks can be made nearby on the north side of Route 33 on Second Mountain and Dictum Ridge.  In 1992, modern climbers re-discovered a formation that resembles the profile of George Washington on Lovers’ Leap, which was a favorite of the old resort visitors.  It was thought to have been dynamited by vandals many years ago.[v]   In winter it can be seen from Route 33.  One notable feature of the rocks is their tortured, massiveness that without climbing can be seen on casual strolls and drives or while taking in a dip in the Dry River.
Water Resources
Dry River
One of the most prominent physical features and one that served as a frequent point of reference for western Rockingham County is the Dry River.  The River begins as a network of small streams (Runs) on the east slope of Shenandoah Mountain and flows through a gap at Rawley Springs and then across the Little North Mountain fault to the North River at Bridgewater.  The Dry River often appears to live up to its name, but the large boulders resting in the river’s path attest to power of the stream during periods of high water and long ago upheavals.
As early as 1807, Dr. Peachy Harrison noted in a scientific paper for the Philadelphia Medical Museum that “this district (Rockingham County)...abounds with perennial springs.  The water they yield holds so much lime…or to use a common phrase, is so hard to require breaking before it is fit to be used in washing clothes...”[vi]  In 1891, much to the delight of the residents of Harrisonburg whose well water was very hard, the Dry River became the City’s primary source of water.  The water of the Dry River is soft.  From this River at Rawley Springs, Harrisonburg received its water by gravity flow by way of a 10 inch cast iron pipeline laid by using a pick and shovel.  By the 1930’s, Harrisonburg’s growing population and the reduced water flow from the River during the summer months caused water shortages.  Allen B. McDaniel, a consulting engineer from Washington, DC, discovered a unique solution to Harrisonburg’s water problem.  He discovered about 15 feet below the River bed a subterranean constant flowing stream running over limestone bedrock.  The underground water source, trapped by an underground dam where the two mountains meet at Rawley Springs, again provided a reliable water source for Harrisonburg. 
There are many well-known springs in Rockingham County.  The springs are the result of a natural flow of ground water to the surface.  They are characterized by a variety of conditions, such as rock type, rock structure, and source of water supply.  At Rawley Springs, three small springs, which issue from a syncline in the Pocono sandstone, are chalybeate, so named because of the peculiar taste due to presence of iron in the water. [vii]  The significance of springs in the history of Rockingham County is another topic for exploration.
 Mineral Resources
Cement, of which limestone is the chief ingredient, is common to the area.  An old lime kiln about two and a half miles southeast of Rawley Springs on the Dry River and many other similar structures around the County are evidence of limestone’s significance in the economy of the area. 
Also, known since at least 1834, a coal-field crop lies on the northwest slope of Narrow Back Mountain that runs from Stokesville in Augusta County to Rawley.[viii]  One of the three County coal locations was near Rawley Springs and was noted on several of its metes and bounds descriptions.  The coal pit was near Union Springs Road. 
            Technical matters aside, collecting rocks is an enjoyable and educational hobby.  On February 23rd at 1:00 at the Main Library, geologist and lapidarist Stuart Mercer of Elk Run Mining will show patrons the gems that await in our county.  
by Diane Rafuse

[i]  In the Courthouse are the Road Books, an invaluable resource that records by mile marker from the Courthouse the person or persons responsible for a portion of the road.
[ii] John W. Wayland.  History of Rockingham County.  C.J. Carrier Company, Harrisonburg VA. 1996.  Originally published 1912. 426-7.
[iii] William B. Brent. Geology and Mineral Resources of Rockingham County. Virginia Division of Mineral Resources. 102.
[iv] Brent. 102.
[v] Zook. 17.
[vi] John W. Wayland. A History of Rockingham County Virginia.  430.
[vii] Brent. 157.
[viii] Brent. 142.