The Geology of Winged Deer Park

Johnson City, Tennessee

 

By:  Robert E. Whittemore, CPG

Chief Geologist, General Shale Brick, Inc.

(RPG TN 3006)

 

 

Welcome to the premiere walking park of the Tri-City area.  The trails of Winged Deer take walkers past an astounding variety of plant assemblages, wildlife habitats, and bird populations.  In addition, these trails and paths will also lead the casual hiker over a fascinating series of clues as to what lies much deeper below the surface, and how it all came to be that way.  Rocks will tell a story if you know how to read their unique language.  The purpose of this hike is to examine a few pages of earth history, demonstrating some of the techniques used in deciphering the code, and to see how one goes about interpreting the record frozen in barely a handful of rock fragments, and from these scraps of information, cause the big picture to emerge.

 

 

A Brief Chronology

 

Reading the chapters of Earth's history as it is recorded in the rocks is like browsing through a book; but because the most recent pages are on top, one must begin at the back cover and work toward the front.  Some of the chapters are generalized and vague, others are rich in fine detail.  Some chapters cover vast eons of time in which seemingly nothing happened, while others are filled with tales of unimaginable violence and catastrophe. 

 

The scientific community estimates the age of the Earth at around 4.5 billion years.  Fortunately, we do not have to probe that far back into the annals of time to find the beginning of the chapter that deals with Winged Deer Park.  In fact, we are only interested in the most recent ten or so percent, but even that is a whopping five hundred million (500,000,000) years.  A major division in geological time is drawn at 544,000,000 years ago when a primitive organism known as archaeocyathid left behind a calcareous skeleton that became a fossil.  All geological time since then is referred to as Phanerozoic.  The first 34,000,000 or so years of the Phanerozoic are known as the Cambrian Period.  This epoch was followed by the Ordovician Period, which lasted from 510,000,000 years ago until 439,000,000 years ago.  It is somewhere near the systemic boundary between the Cambrian and Ordovician periods that the bedrock of Winged Deer Park was being formed.

 

Before you can have sedimentary rocks, however, you need at least three things: (1) a provenance, or source of sediment, (2) accommodation, or a place for it to settle, and (3) a transport mechanism such as wind, water, and gravity.  About 650 million years ago, the North American Continent was part of the pre-Pangeaen supercontinent of Rodinia, which was in the process of tearing itself apart.  The inland areas were getting stretch marks due to being part of an extensional terrane.  Some of these stretch marks ruptured and became faults, allowing parts of the crust to sink lower into the underlying mantle.  When the sections of continent finally separated, a new ocean was born.  It would later become known as the Proto-Atlantic Ocean, now more commonly known as the Iapetus Ocean.  Meanwhile, and much closer to home, some parts of the continental interior were extended enough to sag and become flooded, creating a vast inland sea.  Detrital material, composed mainly of rock fragments of various sizes, was weathered from the Blue Ridge and transported westward into the sea, which resulted in thick sequences of clastic rocks, such as sandstone, shale, and conglomerates to be deposited.  Much later, these massive formations would be lifted high by thrust faulting and exposed by erosion, and can now be seen outcropping along the crest of Iron Mountain and Holston Mountain.

 

The influx of terrigenous, or earth-derived sediments was rapid at first, but as the source area eroded and became less rugged, the supply of sediment slowed to a trickle.  There were few if any plants to slow the erosion, and there was little crustal activity to create new source areas, so the exposed land mass approached level conditions.  Out in the basin, the water became clear, allowing sunlight to penetrate, thus giving rise to the growth of algae and other lime-secreting organisms.  The secretions settled to the bottom in great thicknesses, accumulating to form the massive limestones and dolomites of this region.

 

Five hundred million years ago, the North American Continent was drifting in the equatorial waters of the Iapetus Ocean.  Farther south, across the Iapetus Ocean, was the immense supercontinent of Gondwana.  Just what happened at the sea floor as these two land masses approached each other has been modeled.  As one of these models has it, a peripheral bulge raised vast stretches of carbonate (limestone and dolomite) sediments above sea level.  An irregular erosion surface developed that included sinkholes and caves.  Under further pressure, the bulge sank again, and the caves and sinkholes were filled with more carbonate sediment, but of a different character.

 

By 450 million years ago, the Iapetus Ocean was beginning to close as the North American Continent drifted closer and closer toward Gondwana, taking aim at a portion of the coastline that would be the west coast of South America.  The East Coast of North America was (and still is) what is known as a passive margin of a continent, meaning that it was carried along by the movement of a spreading ocean floor rather than riding up over ocean floor rocks as they are subducted back into the earth's mantle.  Thus, the North American Continent was being pulled along as ocean-floor crust passed below the active margin of Gondwana in much the same way as grocery store purchases are pulled along on a conveyor belt toward the cashier.   These lateral forces caused the inland sea to the west to deepen, and the long period of carbonate deposition in clear, shallow water gave way to black shales in deep, anoxic water.  Occasionally, coarse gravels were eroded rapidly and deposited as conglomerates  as the crust warped in response to the change in plate motion.  This surge of terrigenous sediments, along with the apparent deepening of the basin put an abrupt halt to the production of limestone by sunlight-loving organisms. 

 

The black shale can be seen at any number of grading projects on the southeastern side of the Bristol Highway.  There is an especially good exposure at the Powell Construction site.  Coarse conglomerates outcrop on Masters Knob (site of the big blue water tank and microwave tower that can be seen from almost anywhere in North Johnson City), and in the bluffs on the north side of Boone Lake along Hyder Hill Road, 1.5 to 2 miles east of Rocky Mount.

 

By 400 million years ago, in the vicinity of what is now the New England states, volcanic islands began to collide with the North American continent in a mountain-building event known as the Acadian Orogeny.  Motion along nearly-horizontal thrust faults carried huge tracts of real estate from North Carolina westward, possibly as much as 40 miles.  The faulting was ductile, and the pressures it generated caused much of the folding of otherwise brittle rocks into anticlines (arch-like) and synclines (trough-like).

 

By 250 million years ago, the Iapetus Ocean was essentially gone.  Faulting continued, but was now more shallow and brittle.  During this event (known as the Alleghanian Orogeny), the crust was lifted to great heights where the erosive power of wind and water carved the valleys and landforms we see today.

 

 

A Foreword About the Bedrock of the Park

 

The major rock type found in Winged Deer Park is limestone.  Limestone is a sedimentary rock.  Sedimentary is one of the three major rock classifications, the other two being igneous and metamorphic.  All three types of rock may be found within 30 miles of Johnson City.  Sedimentary rocks are made up of fragments of older rocks, as in sandstone and shale; or a chemical precipitate, as in limestone and dolomite.  Igneous rocks are those that have solidified from the fluid state known as magma.  Metamorphic rocks are those that have changed due to pressure, heat (but not enough heat to return the rock to a fluid state), or by exchange of ions dissolved in fluids, a process known as metasomatism.

 

Rock particles that are eroded from land masses are carried by rivers toward the ocean or a sea.  The river has a certain amount of energy imparted by gravity, so it picks up and carries rock particles along with the water.  A river actually carries three types of load.  There is the bed load, which consists of larger rocks that are transported along the bottom by the force of the current.  Then there is the suspended load, which is mostly sand, silt, and clay-size solid particles kept in suspension or bouncing along the bottom by the river current.  Finally, there is the dissolved load, which is comprised of soluble substances such as sodium chloride and calcium carbonate, that will not be precipitated until a change in chemical composition occurs. 

 

Let us now imagine a shallow sea, such as the Gulf of Mexico, adjacent to a rugged coastline.  Rains fall on the land, and the runoff collects into rivulets, quickly eroding the barren landscape.   Now, imagine a river collecting all three types of load described above, and delivering them into the sea.  Because of the rapid drop in kinetic energy when the coastline is reached, the gravel of the bed load barely clears the mouth of the river.  The sand is deposited not far beyond that, and is carried along the strand line, forming beaches and dunes.  If  these deposits are buried by later deposits, they will become sandstone.  The silt-sized particles wash farther out to sea.  Clay is carried the farthest because of the dipole affinity for water, which will overcome the pull of gravity until several more clay particles join together creating enough mass to begin to settle, eventually to become shale.  Somewhere, out beyond the muddy waters near shore, there is clear water that sunlight can penetrate.  Organisms such as algae and mollusks can grow and thrive in this water. As they do, they secrete or cause to precipitate calcium carbonate, which begins as a thick ooze on the sea floor, but eventually solidifies into limestone.

 

Occasionally, there is an abundance of magnesium salts dissolved in the sea water.  Some of these ions react with the limestone, partially replacing the calcium and creating dolomite.  Collectively, limestone and dolomite are known as carbonate rocks.  Please note that there is also a mineral by the name of dolomite, so many geologists -- mostly the younger ones -- have begun referring to the rock as dolostone.

 

 

 

A Walking Tour of the Geology of Winged Deer Park

 

Now that you are aware of the overall picture of what is under your feet in the park, it is time to examine some of the more interesting, and quite possibly surprising details.  The sites you will visit are in a "shortest path" order, but may be visited in any order.  The stop numbers are shown on the accompanying geology map, and the last paragraph below explains the other symbols used.  The minimum hiking distance is about 2.5 miles (4k), so plan accordingly.  If you are not on one of the Park-sanctioned hikes, there may be a detailed trail log attached.

 

Stop #1 -- Stones will not cry out, but rocks will tell a story:  Examine the prominent limestone outcrop on the hill near the picnic table.  You may notice that it has a layered structure.  This is to be expected in a sedimentary rock, and the layers are presumed to be originally horizontal.  Each layer, as well as the partings, or discontinuities, that separate it from its lower and upper neighbors, may yield bits of information about the conditions under which it was deposited.  Often such an evaluation requires microscopic studies or a detailed chemical analysis, but here you will find at least one horizon that reads easier than most.  Look on the west side of the outcrop (that is the side away from the Bristol Highway), and look closely at one layer that is about six inches from the top.  You may notice a faint, gray-on-gray pattern, with the lighter gray domains suspended in a darker gray matrix.  The lighter gray domains are most likely the edge-on view of mud flakes from a tidal flat or other such area that was shallow enough to dry up occasionally.  Cracks would then form on the upper surface of the still-soft lime mud.  When the water rose again, it swept over the tidal flats, picking up and transporting fragments of the dry, mud-cracked surface as it went.  That is one possible explanation.  Perhaps you can come up with another.

 

 

Stop #2 -- Cross Stratification, and Rillenkarren:  This outcrop is in the yard of the Park Headquarters.  Again, you will find what appears to be an ordinary gray limestone outcrop.  But, upon closer examination you will find that it has recorded a slice of time in one of its ledges.  Notice the way the finer, diagonal lines meet the stronger bedding planes at a shallow angle.  This pattern is characteristic of shallow water flooding a tidal flat.  Wherever a small drop-off occurs, sediment is deposited on the downstream side, gradually building a new layer of sediment, accreting in the direction of flow and raising the tidal flat by its thickness.  Look closely at the darker, fine lines separating the cross-beds (using a magnifying glass if you have one) and you will notice a thin layer of sand grains, some of which stand out in relief due to weathering of the limestone. The segregation of sand into the discontinuities tells us that the energy of the source-area environment was pulsing, probably due to tides. In some outcrop situations, it is possible to measure the attitude of the cross-stratification and determine the direction to the source of the current and sediment. 

Examine the weathered surface of this outcrop as well as others in the immediate vicinity.  Some of the surfaces display a mode of weathering known as rillenkarren (sorry, there is no synonymous colloquial term, so we are stuck with this mouthful).  Rillenkarren are fine, parallel runnels or grooves with rounded troughs and sharp ridges.  They are usually 1/2 to one inch deep, and are best developed near the crest of the outcrop where rainwater is more highly charged with CO2.  They occur mostly on limestone, rarely on dolomite.

 

 

Stop # 3 -- Soil Erosion:  Earth moving activity associated with construction or mining as well as some agricultural practices leave soil exposed on steep banks or loose outslopes.  Stormwater runoff dislodges soil particles, which in turn impact other particles, breaking them loose from the ground.  Small rivulets form, then larger gullies, carrying precious topsoil and subsoil away into rivers where it is transported to the sea or to settle behind a hydroelectric dam.  To most of us, this is a careless and wasteful practice that should be eliminated.  While they last, however, a field geologist may take advantage of these bare, exposed areas to steal a glimpse into the subsurface.  To the trained eye, much can be learned.  From where, for example, does all this clay-like soil come?  As the limestone bedrock weathers away, insoluble particles -- mostly clay -- that were trapped inside the limestone are liberated.  Gradually a blanket of clay and silt that may be quite thin or prodigiously thick will develop.  Where this clay blanket is formed in place and retains traces of primary rock features, it is known as saprolite.  If it has been transported, it is called colluvium.  Together, these unconsolidated deposits are known as regolith.

 

Digging around in one of these bare areas may uncover some clues to what occurs at depth.  For example, in any given bare area, we may find larger rock fragments randomly distributed throughout the clay matrix.  We would be likely to find (1) well-rounded, smooth quartzite rocks, (2) angular sandstone fragments, and (3) gray to black, hard, flinty nodules.  The major content of all three of these is silica, which is the basis of quartz, one of the most persistent minerals in nature.  The rounded rocks acquire their shape from being transported by water, and most likely represent the bed load of the Watauga River in the distant past when it occupied a higher level before eroding down to the level we see it today.  The angular sandstone fragments have not been transported; otherwise they wouldn't be quite so sharp-edged.  These fragments probably occurred in the bedrock as a thin sandstone unit interbedded with the local carbonate rocks (limestone and dolomite).  Resistant rocks left behind in a clay matrix like this are known as float.  The hard, grainless, flinty nodules, known as chert, are formed in the bedrock by a different process that is not well understood.  The typically nodular shape would suggest that the silica was segregated from the carbonate sludge, not unlike oil and vinegar in your salad dressing. The silica then coagulated at a neutral buoyancy horizon in the sediment column.  As the sludge continued to accumulate, the deeper zones were packed tighter and tighter, forcing out the water, but locking the solid matter in place to be lithified, or changed into rock.

 

 

Stop #4 -- Top of Huff 'n' Puff Hill, and a Possible Marker Horizon:  Ever wonder why a hill is where it is?  Often, it is because something has protected it from erosion.  That something could be a layer of hard rock that is thicker or more resistant at the hill, or it could be a thick deposit of coarse gravel that acts as an armor plate against the erosive forces.  A search around the top of this hill reveals that a ledge of sandstone may have served in such a manner. 

 

But there is another way in which we can exploit the location of this ledge:  we can use it as a marker horizon.  A marker, or index horizon is a stratum, or layer, of rock that is different enough from the rest of the local bedrock that it can be traced from outcrop to outcrop, thus allowing for a more accurate interpretation of the structure.  To qualify as an index horizon, the rock interval must be easy to identify, it must be continuous and persistent, and very importantly, it must be unique.  Examples of index horizons include blankets of volcanic ash, any sharp contact between two different rock types (as long as there is only one transition in either vertical direction), sudden appearances or disappearances of fossils, or a narrow zone of concentration of a particular mineral.  It could even include a horizon of meteorite impact ejecta.

 

The sandstone ledge was probably the result of the collapse of an advancing delta front due to a storm or earthquake.  A river discharging into a shallow sea gradually builds a delta of sediment that it no longer has the energy to transport.  Often, the delta grows rapidly and the advancing front becomes oversteepened.  An earth tremor or storm event may destabilize the outermost part of the delta, sending a powerful surge of coarse sediment in an underwater avalanche toward the deeper regions of the sea.  Gradually the sand settles to the bottom, resulting in a unique layer of sand among the many layers of limestone or shale.

 

A problem with this particular sand ledge is, there is nothing to distinguish it as the only sand ledge in this area.  If there is more than one, then trying to correlate the different outcrops can lead to an erroneous picture of the rock structure.  The fact that we do not see another ledge nearby isn't enough to go on.  Lack of evidence is not evidence of lack.  We can hedge our bet a little by noting certain details, such as why this ledge is not the same one we examined at Stop #2, which has a predominantly limestone matrix.

 

 

Stop #5 -- Cave:  The opening at the bottom of the sinkhole gives access to a small cave with about 380 feet of passage (map attached).  The unabraded surface of the passage walls and the clay-like deposits along the floor suggest that the cave was formed below the water table, in the phreatic, or saturated zone where the horizontal movement of water was very slow.  The passages began as joints in the limestone, and were enlarged by dissolution by acid-bearing water. 

 

The cave passages were enlarged a second time by removal of the cave floor deposits in one of two mining operations that have occurred in Winged Deer Park during historic times.  The clay floors of this and many other area caves contain a water-soluble component that was once essential to the manufacture of gunpowder.  The component yielded by cave dirt was calcium nitrate, which, when combined with potassium hydroxide, produced potassium nitrate, also known as saltpeter.  The saltpeter was then blended at 75% with sulfur (15%) and charcoal (10%) to make black powder used extensively in explosives and firearms prior to 1884 and the invention of smokeless powder.

 

Evidence that the cave was mined for saltpeter is found in (1) the footlogs over chasms near the entrance, (2) heavy soot stains on the roof as a result of burning pine torches for light, (3) changes in floor level where digging became difficult, and (4) small piles and stacks of loose rock along passage walls, separated by hand from the soil.

 

The dirt was taken from the cave and placed in a hopper-like vat where it was saturated with water to leach out the nitrate. When the dirt had soaked long enough, the leachate  was then drained off at the bottom.  Wood ashes were also leached in a similar manner.  When the two leachates were combined, the calcium hydroxide was precipitated, and the potassium nitrate, or saltpeter, was held in solution.  This solution was then boiled to concentrate the saltpeter, which was skimmed off the surface.  The concentrate was melted again to drive impurities to the surface, which were also skimmed off by hand.  The production of saltpeter was an important peacetime cottage industry, furnishing powder needed for hunting, quarrying, and road construction.  During times of armed conflict, saltpeter naturally became a critical strategic material.

 

 

Stop #6 -- Sinkholes:  The word “sinkhole” has various meanings around the country, but in this context we'll accept the widespread local usage and define sinkholes as topographic depressions that result from the dissolution of limestone or other carbonate rock.  They may, but do not necessarily, have a cave entrance.

 

There are three general categories of sinkhole based on their morphology, or form.  The most common type is the solutional sinkhole.  They are shallow, saucer-shaped depressions caused by a higher density of joints, or rock fractures, in an area which in turn results in more rapid dissolution of the bedrock.  The alluvial sinkhole is less common in this area, but they do exist here.  They occur where thick, alluvial overburden gradually slumps downward through open joints into a void below.  This kind of sinkhole is usually narrow with steep sides, often with bare soil showing.  And then there is the perennial bad actor, the collapse sinkhole, that wasn't there yesterday, but today it is where the henhouse used to be.

 

As you pass some of the sinkholes that are plentiful in the wooded areas, you may notice that more than a few are characterized by a small area that has slumped enough to show bare soil.  What kind of sinkhole is that, and what is it doing here?

 

 

Stop #7 -- Dolomite or Dolostone:  A close inspection of the rock outcrops in this area will reveal that some of the ledges are quite different in appearance from adjacent ledges.  The non-typical ledges (1) weather to a buff or tan color, (2) have a finely-jointed, or "butcher block" pattern on exposed surfaces, and (3) are lighter colored on a fresh surface than the surrounding limestone.  These are ledges of dolomite.  In spite of the rather outstanding differences we see here, none of them are a foolproof  means of distinguishing dolomite from limestone.  In order to determine which is which, we must place a grain of rock in a solution of dilute hydrochloric acid.  If it fizzes, it is limestone.  If not, then it is dolomite.  For expediency, most field geologists simply squirt a few drops of acid on a fresh surface to see if it reacts, but care must be taken to insure that the fizz is not coming from a paper-thin, calcite-filled joint, or a powder-fine residue of dolomite dust produced by hammering, which will produce a fizz if it is pulverized finely enough. 

 

Dolomite (or dolostone) is similar to limestone in that they are both carbonate rocks.  The chemical composition for limestone is CaCO3 and for dolomite is Ca,Mg(CO3) 2.  Dolomite is thought to occur when calcium (Ca) ions are replaced by magnesium (Mg) ions during the formative stages of limestone.  Since the Ca ions are larger than the Mg ions, the resulting dolomite is more brittle and finely jointed.

 

Note also the black chert nodules standing in relief and occupying the same stratigraphic level.  Their flinty composition makes them more resistant to weathering than the host rock.

 

During Middle Ordovician time, approximately half a billion years ago, either the sea level dropped, or the land was uplifted.  Either way, not much change was needed to expose the sea floor to erosion, since the sea was evidently very shallow.  Dolomite forms more readily in warm, shallow water where evaporative loss tends to concentrate the magnesium.  Once the waters receded, erosion occurred rapidly, since there were no known plants on land at that time.  A rugged terrain resulted, with river channels, hills, sinkholes, and even caves.  Later, the sea returned and the dolomite landscape was buried beneath many hundreds of feet of limestone.  The old erosion surface is now referred to in this region as the Knox-Middle Ordovician disconformity.  It is not well exposed in this area; however, we may catch a glimpse of it at Stop #10.

 

 

Stop #8 -- Anticline:  At most of the limestone outcrops we have examined thus far, we have observed that the bedding planes dip to the southeast, back toward the Bristol Highway.  Now, as we cross the sinkhole valley and begin to climb the hill on the other side, we notice that the ledges of rock are slanting away from the center of the valley and toward the northwest.  If this trend continues, it means that we have crossed the axis of an anticline, or an arch-like, upward fold in the bedrock.

 

 

Stop #9 -- Sandstone Ledge, Again:  Continuing up the trail, a sandstone ledge is encountered.  It looks very much like the one we saw at the top of Huff-and-Puff Hill, and in fact it may be the same one.  Unfortunately, we have no irrefutable means of identifying it as the same ledge.  So, we must maintain two working hypotheses:  (1) it is the same ledge, and (2) it isn't the same ledge.

 

Another 100 yards or so to the west along the fenceline trail will bring you to the top of a hill at the western corner of the park.  The elevation here is about 1640 feet above sea level, which makes it the highest point in the park.  If one were to scrounge carefully among the few loose rocks lying about the surface (the poison ivy is lush here in the summer), one would most likely find that they are all sandstone.  Obviously, they did not roll down hill to arrive at this location, so now we can modify our hypothesis -- there are at least two sandstone ledges.

 

 

Stop #10 -- Rock Outcrop in Back Parking Lot:  This small exposure shows some interesting features.  At the bottom, the rock is a light gray dolomite.  The bedding is nearly horizontal.  The top, however, is a dark gray limestone with rounded carbonate clasts.  The bedding in the upper unit is far from level, and it truncates the flat bedding of the lower unit.  Quite possibly, this is a section of a scour channel that was subsequently filled with coarser sediments.  There is not enough outcrop here to determine the extent of this discontinuity, but the Knox-Middle Ordovician disconformity is not ruled out.

 

Stop #11 -- Rounded Rocks in Overburden:  Here along the trail between the Frisbee golf course links, you will find many loose rocks on the surface.  These rocks are characteristically rounded and stained from having been transported by water as a bed load.  Today we do not see a stream in this valley with enough flow to move rocks this size very far, or to tumble them enough to achieve their distinctive roundness.  Even searching the cave does not yield a powerful enough transport mechanism.  But, by examining the topographic map, one could conclude that the Watauga River flowed through this valley some time ago, leaving river bed deposits in its path before abandoning this channel for the one it occupies today.  Anyone attempting to stand on this spot 10,000 years ago would be treading water.  Ten thousand years ago is a wild guess, but it approximates the height of the last Ice Age.  Although there were no known glaciers in this region, the rainfall and the river's erosive power were greater.  Today's river level is 100 to 105 feet lower than this deposit of river rocks.

 

At this point, you may recall from Stop #6 that many of the sinkholes in the wooded area of the park showed steep, bare-soil sides typical of alluvial sinkholes.  Now that the source of the alluvium can be explained, so can the morphology of the sinkholes.

 

 

Stop #12 -- Old Railroad Cut:  Artificial exposures such as this one often provide the best opportunity for understanding the geologic structure and the stratagraphic sequence.  Several questions have been raised so far; like, is there more than one marker horizon; is the anticline an important structural feature, or just a local flexure?  If only one sandstone ledge can be located in this railroad cut, we may be able to draw our own conclusions based upon our experience and observations.

 

Historical comment:  This railroad cut was part of a railroad line begun by the CCC -- Charleston, Cincinnati, and Chicago Railroad -- back in 1886.  General John H. Wilder of Cloudland Hotel and Roan Mountain fame was the Company's Vice President.  The depot was to be on Broadway Street in Johnson City, near the other railroads in the area.  Although over 70 miles of roadbed was constructed, only a few miles of track were laid, mostly between Johnson City and Erwin.  The abandoned roadbed can be traced through town where it is now occupied by portions of Fairview Avenue, Lakeview Drive, and Cash Hollow Road.  The roadbed is quite possibly the longest stretch of never-used railroad bed in the country.  The 3-C Railroad failed during the panic of 1893, and its assets were purchased by the Clinchfield Railroad.  Work on the grade was never resumed.

 

 

Stop #13 -- View of Anticline Across Boone Lake:  Unless the water is too high, we should now be able to pick out the anticline as we look along its axis at the bare, steep shoreline where wave action has stripped the topsoil away from the bank, leaving the bedrock exposed.  By extrapolation, we should look for an arch-like structure, but instead we have a surprise waiting. 

 

Instead of a single arch, there is the suggestion of a small syncline along the crest.  If the water in the lake is low enough, several domains of nearby outcrop will show angles and directions of dip that do not seem to fit the rest of the picture.  Looking back at the dip & strike map, there are a number of symbols, usually with single-digit dips, that appear to be out of place.  This seeming discrepancy is explained by the exposure on the far side of the lake.  Notice how some large areas near the crest of the arch are missing, or breached.  The bending of the strata is sharper on the node of a fold structure, which leads to more intense fracturing as well as small-scale faulting and folding.  This is especially prevalent in rigid, brittle rocks like limestone and dolomite (a.k.a. dolostone), which causes that area to be more susceptible to weathering and erosion.  Sandstone, with its grainy fabric that is able to absorb and to accommodate deformation, is more likely to bend smoothly.  Shale, on the other hand, is more flexible yet weak, and is likely to show intense, small-scale folding and a variety of other structures.

 

Stop #14 -- Secondary Deposits:  Between the lake and Carroll Creek Road is an expanse of turf with no discernible outcrops of rock.  The bedrock here is covered by alluvium, or leftover products of dissolution from the limestone upslope, and fluvial, or river-transported deposits from upstream.  Areas such as this were attractive homestead sites to the early settlers.  The terrain was reasonably level and the soil tillable, and water was readily available.  Wells dug down to the contact between the river deposits and bedrock were virtually assured of producing potable water.

 

Note:  a careful search along the roadcut in the vicinity of the second utility pole west of the driveway to the maintenance building may pinpoint the possible sandstone ledge marker horizon, thus closing the loop on our observations.

 

 

Stop #15 - Quarry and Lime Kiln:  About half way between the lake access road and the Bristol highway, and on the south side of Carroll Creek Road is a small quarry; the second of two mining operations that have occurred on Park property.  It appears that the stone from this small working face was extracted by hand.  The slabs of limestone that were levered out were likely broken into small pieces and fired in a charcoal furnace to produce agricultural lime.  The burned, calcined lime was spread over the fields to react with acids in the soil, raise the pH, and thereby improve growing conditions.

 

 

Attached geology map -- how to read and translate:  The geology map is the single most important document by which the geologist communicates his findings.  The map included here uses standard symbols.  First, notice the T-shaped symbols with an accompanying number.  The crossbar of the T traces the strike, which is the direction of a line along which compositional bedding would intersect an imaginary horizontal plane.  It is a good indicator of the immediate structural trend.  The vertical part of the T points down-slope and perpendicular to the strike in the direction of the dip, or maximum angle the rock bedding plane surface would make with a horizontal surface.  The small number near the T indicates the angle of the dip in degrees.

 

Dolomite measurements are colored green, blue symbols represent limestone, and red indicates sandstone. The line of red-colored dots shows where a certain sandstone marker horizon lies at the surface.   The heavy black line to the left of center is the trace of the axis of the anticline. 

 

The bold numbers show the location of the stops referenced in the text above. 

 

 

 

Acknowledgements:

 

This article was prepared under the auspices of Brad Jones, Ranger/Naturalist, Johnson City Department of Parks and Recreation.  The writer wishes to acknowledge the expert field assistance of Anne Whittemore.  Ingrid Luffman, hydrogeologist and adjunct instructor at East Tennessee State University proofread the manuscript and offered many valuable suggestions.

 

Robert E. Whittemore

Gray, Tennessee

June 1, 2002

 

 

References:

 

Butts, Charles, 1940, Geology of the Appalachian Valley in Virginia, Part I -- Geologic Text and Illustrations:  Virginia Geological Survey, Bulletin 52, 567 pages.

 

Faust, Burton, 1955, Saltpeter mining tools used in caves:  National Speleological Society, Bulletin 17, pages 8-18.

 

Frye, Keith, 1986, Roadside Geology of Virginia:  Mountain Press Publishing Company, Missoula, Montana, 278 pages.

 

Hardeman, W. D., 1966, Geologic Map of Tennessee:  State of Tennessee, Department of Conservation, Division of Geology, 4 sheets, in color.

 

Imbrie, John, and Imbrie, Katherine Palmer, 1979, Ice Ages; Solving the Mystery:  Enslow Publishers, Short Hills, New Jersey, 224 pages.

 

King, P. B., et al., 1944, Geology and Manganese Deposits of Northeastern Tennessee:  State of Tennessee, Department of Conservation, Division of Geology, Bulletin 52.

 

Pan Terra, Inc., 1994, A Correlated History of Earth:  Pan Terra, Inc., Afton, Minnesota, one sheet, 27" x 38" with explanatory text.

 

Rodgers, John, 1953, Geologic Map of East Tennessee with explanatory text:  State of Tennessee, Department of  Conservation, Division of Geology, Bulletin 58, 168 pages.

 

Sweeting, Marjorie M., 1973, Karst Landforms:  Columbia University Press, New York, New York, 362 pages.

 

 

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