Regional topography

The Cumberland Plateau

Franklin County is a spectacularly beautiful part of Tennessee. It lies across the western edge of the Cumberland Plateau and the broad valley of the Elk River and its tributaries. The local topography generates sharp contrasts between valley and plateau at every turn. From the plateau, scenic vistas open in every direction. From the valley, there appears to be a surrounding rim of mountains. The forest resources and soils characteristic of each zone generated very different lifestyles among settlers. The upcountry of the plateau merged almost seamlessly with the lifestyle of the Scotch-Irish settlers of the Appalachian mountains to the east. In the fertile soils of the southwestern end of the county, large acreages could be carved from the broad, flat valley floor, and this area of the county saw the upper limit of Tennessee Valley cotton planting in the Nineteenth Century. An early social tension developed between the subsistence gardening-hunting folk of the plateau and coves and the farmer-planter culture of the lower county.

The Cumberland Plateau is the regionally large rock shelf that abuts the Cumberland Mountains on their western side. The plateau averages about 2000 feet in elevation, characterized by a nearly flat top with thin soils, and edged by an escarpment or series of cliffs. The cliffs average 50 feet in direct fall but may be as high as 150 feet or more. The escarpment is broken or eroded by numerous streams creating what geologists call "nick points" where the stream erodes the upper edge of the escarpment. These stream courses through the escarpment are often the location of trails or roads that reach up from the valley to the plateau. Locally the Cumberland Plateau is composed of layers of shale and limestone below and a thick cap of sandstone above. In some areas there are also seams of coal inter layered in the sandstone. The local strip-mines result when the easily fractured "overburden" of sandstone and conglomerate is scooped aside to get at the underlying coal seams.

The sandstone has traditionally been quarried for attractive building materials. Sometimes the sandstone fragments into layers and the layers are levered apart and the resulting rock slabs are broken into construction size pieces. This kind of sandstone is occasionally referred to as Tennessee field stone. It is used for house construction as well as for walkway surfaces and edging. Collection and shipping of this loose stone constitutes a minor cottage industry at a few places around the plateau. Sandstone is also sawed into regular blocks for precise building construction as in the buildings of the University of the South. On the Perimeter Trail and at a few other places on the Domain of the University, the indentations of small sandstone quarries can still be seen. Near Otey Prospect the drill marks from earlier quarrying are still visible in the sandstone.

In the coves of the plateau, erosion has broken the sandstone cap and over time the fractured sandstone has been tumbled in the stream beds. This tumbled sandstone is often melon sized and is sometimes used for garden edges or for building materials. St. John's Church in Ladd Cove off of Battle Creek is constructed of this stone taken from the nearby creekbed. The rounded rocks that line the bottoms of streams like Battle Creek and the Little Sequachie River in nearby Coppinger Cove are this tumbled sandstone. Coated with algae, the rounded form of these rocks make for very difficult wading conditions for anglers. These are also the typical rocks found in the many dry stream beds leading from the coves to the perennial streams.

Some parts of the sandstone cap of the plateau contain deposits of unconsolidated sand along with small gravel locally known as "pea gravel." This sand is mined near Sewanee at the "sand plant" along Rt. 41 toward Monteagle. The pea gravel is locally used for walkways, either loose as in the walkway at Rebel's Rest or mixed with cement which is washed before curing to produce the common "aggregate" sidewalks of the University of the South. Pea gravel is also frequently specified as the fill material for the sandboxes and playground areas of daycare centers and kindergartens. On occasion, sand is prepared by crushing the soft sandstone. On the Jumpoff Road near Orme there is currently an active "strip mine" where sandstone is being quarried for this purpose.

The seam between the limestone layer below and the sandstone layer above is the zone of an interesting and significant geological interaction. Water dripping through the sandstone begins to move laterally when it encounters the limestone. Over time, the limestone is dissolved thus creating the familiar caves of the region. Ranging from small tubular openings in the limestone to huge underground caverns reaching for miles, the Cumberland Plateau area is home to some of the most interesting speological sites in North America. The constant temperature of these caves at about 54°F, along with an associated stream made the caves important Amerindian gathering sites. While nearby Russell Cave in Doran Cove is nationally famous for the antiquity of its Amerindian remains, many other caves in the region were also used by the Indians.

The limestone in the lower levels of the plateau often supplies building material--concrete--when processed or construction material--"gravel" in local usage--when crushed. A number of limestone quarries are located around the region, the largest seen on I-24 approaching Chattanooga from the west. Smaller quarries in Franklin County are located in Cowan, near Decherd on Rt. 50, and below Sherwood. A carefully managed quarry is located along Rt. 41 in Moore County near the Shofner Lutheran Church. The crushed rock lining many of the walkways and roadways of the region are generally composed of this limestone. In the valley, but generally not on the plateau the limestone is also used for fences, edging, and residential building material.

For many years a locally important use of limestone was in the preparation of slaked lime and cement. The old limestone quarry in Sherwood is visible just south of the town on the left. In Cowan, Marquette Cement Company operated for many years a cement producing plant in conjunction with the limestone quarry. The remains of the cement plant when viewed from the Cross or Morgan's Steep at Sewanee give Cowan the appearance of a heavily industrial town. The cylindrical towers of the cement plant may remind others of the grain silos of the midwest.

The alkaline soils associated with the limestone are favored by the eastern cedar which can be seen in the winter after leaf fall as a dark green band winding around the escarpment slope about two-thirds of the way down from the top of the plateau. The local availability of this cedar led to an important American industry centered in nearby Shelbyville: the manufacture of pencils.

Coves

An important feature of the Cumberland Plateau is the incisive weathering of the plateau along the irregular line of the receding nick points of the many streams that drain from the plateau. Over tens of thousands of years, this weathering has carved the great stratum of the plateau into hundreds upon hundreds of narrow, steep-sided coves each drained by one or more streams. The decomposed rock of the plateau and the eroding humus of the forest accumulates in the floor of the cove as fertile soil. The soil of the cove floor combined with the natural corral of the escarpment and the rich mast crop of the trees in the coves attracted early settlers.

The nineteenth century economy of cove husbandry was almost entirely invisible. Few travelers visited or penetrated the coves and most observers noted the rundown cabins at the foot of the mountains not realizing the invisible capital represented by livestock roaming in the cove forests. Although John Muir was a great naturalist, on his journey across the Cumberland Plateau, he completely missed the point of this invisible wealth. In his haste to compare the lifestyle of the local residents with the visibly affluent farms of Wisconsin, he noted the poor cabins, the "backward" views, and dearth of material comforts, but he never mentions nor understands the system of livestock management that prevailed in the coves. Together, this livestock and the associated support of valley farmers who grew grain to feed the livestock as they were driven to market, constituted an economic complex in the 1840-1860 period that was annually of more value in the south than the far more visible and notorious "King Cotton".

There is another feature of the topography of the coves that affected early settlers and remains important today. The relatively thin soils of the plateau did not hold much water during heavy rains. Rainfall tends to cascade rapidly from the plateau into the coves below. In times of heavy rain, the cove streams become violent flash flood corridors inundating the valley floor--while depositing a renewing load of sediment from above--and often eroding stream courses. Settlers soon learned not to locate houses immediately along the cove streams but to build upon the first "bench" or leveling of the slope just above the streams. Today, if you walk these benches in the springtime, the blooming of daffodils may be the only surviving reminder of the first houses in these coves.

Regional weather

One does not have to live very long in the Franklin County area to learn that local variations in weather can be extreme--and that the TV forecasting in Huntsville, Chattanooga, and Nashville are of little help. In general terms, local weather is the outcome of the interaction between moisture from the Gulf of Mexico and cold fronts that sweep across the region from northwest to southeast. The average rainfall in the area is around 50" and occasional annual rainfalls of 70" or more have been recorded in the last twenty years. Most of this rain falls between November and April--the rainy season--while the period from June to October is comparatively dry. Temperatures are generally moderate and pleasant: summer temperatures reach the mid 90's in the valley, the upper 80's to low 90's on the plateau. Winter temperatures typically range down to the mid to lower 20's with short periods of zero or sub-zero temperatures in some winters. In 1985 a brief period of unusually cold weather dropped valley temperatures to -18°F, and one location on Sewanee mountain recorded a -26°F temperature. [There was a particular consequence of this sharp cold spike that can still be inferred today: before 1985, there were a number of mimosa trees and magnolias in Sewanee. These trees were mostly killed by the deep cold. The magnolias in Sewanee today--with a couple of exceptions--are trees that have been planted since 1985. Very few mimosas have regenerated since that time.]

Temperatures on the plateau tend to be a few degrees lower than temperatures of the nearby valley. On damp mornings or in periods of high humidity, the plateau will often experience fog while the valley remains clear. During the winter months the plateau experiences another kind of "fog" which is sometimes called "hill fog;" this fog is actually low-level cloud masses which can produce visibilities of less than 100 feet. These stagnant cloud masses may persist for days or weeks during January and February but generally dissipate by the beginning of March. The temperature differential can become critical during winter when there is precipitation and the temperature is around 34°F. In the valley, this precipitation will fall as rain while on the plateau which is just a couple of degrees cooler, the precipitation will fall as snow. During February of 1996 Sewanee received an 8" snowfall in one evening while the valley areas of Franklin County received only rain. Because of this temperature differential, local valley schools experience "snow day" vacations when most of the streets and roads are completely clear. On average throughout the county, annual snowfall is just a few inches and in some years only a dusting of snow is experienced. The plateau sees snow each winter but the usual snowfall is more commonly a dusting or 1-2". The great spring storm of 1993 generated about 18" of snow in Franklin County, but meterologic events of this magnitude are rare.

In the summer months, particularly August, the stagnant humid air mass of the southeast produces a thick haze over Franklin County. The normal view from Winchester offers a ring of "mountains" in every direction except the southwest. In August, from any vantage point in Winchester the plateau may be nearly invisible because of the haze. In periods of unusual heat and humidity, the plateau at Sewanee will be invisible from Cowan near the foot of the mountain. At the same time, the view from the plateau gives the appearance of a much higher elevation because so little if any of the valley floor is visible. By mid-September the restoration of cyclic frontal passages from the northwest sweeps out the humidity and haze and the great vistas of plateau and valley return under crisp blue skies.

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