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]
Geology
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.
Stratigraphy
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
|
||||||||
Million
|
Age
|
Name
|
Symbol
|
Character
|
Thickness
|
|||
Years
|
in feet
|
|||||||
299-251
|
Permian
|
Appalachian
Mtn Fold
|
||||||
Carboniferous
|
||||||||
323-299
|
Pennsylvania
|
Coal
and Sandstone
|
||||||
359-323
|
Mississippian
|
Pocono
formation
|
Mp
|
Massive
white-grey sandstone with
|
300+
|
|||
some
dark shale
|
||||||||
Upper
Devonian Period - Sandstone and Shale
|
||||||||
383-358
|
Devonian
|
Hampshire
Formation
|
Dhs
|
Chiefly
red sandstone, some flag-
|
2000
|
|||
stone,
shales, and mudrock
|
||||||||
Chemung
formation
|
Dch
|
Grey
to greensih silty sandstone and
|
2000
|
|||||
brown
to grey shale, fossiliferous
|
||||||||
Brallier
Shale
|
Db
|
Greenish
brown stiff micaceous
|
1200
|
|||||
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.
Springs
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
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.
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