The Regional Review

Volume I - No. 6

December, 1938


By Donald C. Hazlett,
Assistant Inspector

Since the Mammoth Cave of Kentucky was first opened to visitors in 1816, it has been estimated that more than a million persons have viewed its wonders. While most of these visitors have made the pilgrimage mainly for the novelty and the scenery which the Cave affords, some have gone there for scientific purposes; yet all have been impressed with the Cave's great magnitude--its voluminous chambers and its seemingly endless avenues. To all those who have trodden its famous passageways and observed the numerous cross passages, some of them merely crawl-ways, where eternal darkness and mystery reign, the announcement of the discovery October 9, 1938, of a great new passage did not come as a surprise.

cave formation
18-Inch Gypsum Spiral in Newly Found Section

In discussing this new discovery an attempt will be made to explain the manner in which Mammoth Cave was formed and to describe some of the most outstanding features found in it.

Mammoth Cave National Park lies in the south-Central part of Kentucky in Edmondson, Hart and Barren Counties. The absence of surface streams is one of the striking features of the region. Rain which fails on the surface drains into sinks and flows in underground channels to Green River, the only openly running stream in the immediate area. Such a drainage system is characteristic of limestone regions, and a sink hole topography is an accurate indicator of a cave area.

The limestone in which Mammoth Cave has been developed was formed in the sea which covered the area in early Carboniferous time. This limestone is composed of two formations, the Gasper oolite and the St. Genevieve limestone*, which have a combined thickness of about 250 feet. During Pennsylvanian time a great thickness of coarse sediment was deposited on top of this limestone. At a much later date -- following a regional uplift -- these conglomeratic beds were eroded, and the gravels which are found on the higher hills today probably represent the level at which Green River once flowed. As a new cycle of erosion started and this stream began down-cutting in the limestone, solution channels were afforded which initiated the formation of Mammoth Cave.

Geologically, Mammoth Cave is very young, dating probably from the glacial epoch. It was formed during the last erosion cycle -- while Green River was eroding its present valley. Like all limestone caverns, it owes its entire formation to the slow action of rain or carbonated water upon the limestone strata in which it occurs. While limestone, composed largely of calcium carbonate, is only slightly soluble in water, it be comes much more soluble in water which contains carbon dioxide or organic acids. Rain water charged with carbon dioxide absorbed from the atmosphere and leached from decaying vegetable matter on the surface is able therefore to dissolve the limestone and carry it downward.

Thus, as rain water trickled down through crevices or joints of the limestone and flowed horizontally along bedding planes, gradually dissolving some of the limestone as it went, the passageways were enlarged until good-sized streams could enter. The process of erosion or abrasion was then added to that of the solvent action of water, and the enlargement of the passages went on much more rapidly. Such enlargement, however, depended upon several variable factors -- the amount and character of the sediment carried by the streams, the resistance and comparative solubility of the limestone, the volume and rate of flow of the water in the passages, etc.

As Green River deepened its valley, the underground streams which drained into it either cut their passages vertically downward, forming what resemble box canyons, or they abandoned them as new channels were opened and enlarged at a lower level. Four of the five levels in Mammoth Cave represent these abandoned channels; the highest level is the oldest and probably was formed when Green River was flowing in a shallow valley; on the fifth, or lowest, level is Echo River, one of the present active streams.

Echo River, as well as the other streams in Mammoth Cave, has a special fascination for many people. Visitors thrill at the thought of taking a boat ride 300 feet beneath the surface. The river is 20 to 60 feet wide, 10 to 30 feet deep, and may be explored by boat for several miles before the ceiling becomes too low to allow passage. It flows through a symmetrically-arched corridor 10 to 35 feet high during the dry seasons. In its waters are found blind fish -- fish that have lived in darkness for so many generations that they have become sightless. Other creatures to be seen in the damper and less frequented portions of the Cave include blind crickets, which make their way along the walls with the help of long sensitive feelers, and mollusks, beetles, spiders, worms, crustaceans and cave rats. Bats also spend a part of their time in the cave and may be seen flying about in some of the avenues or hanging, head downward, from the ceiling.

cave formation
Stalactites, Stalagmites, Columns and Flowstone in Violet City.

Some of the most interesting features in Mammoth Cave owe their existence to solution and abrasion. The visitor may walk miles and miles through meandering subterranean stream channels which bear striking resemblance to canyons, although roofed over by rock and thus protected from the usual agencies of weathering. In many places the walls of these channels are vertical; in others, where the streams worked laterally, the walls now overhang the stream beds. One of the finest examples of such a channel is The Narrows, or Beckey's Alley. This narrow slit in the rocks is in places only 18 inches wide while its walls are 50 to 80 feet high.

Perhaps the most impressive features resulting from solution and abrasion are the pits and domes, of which nearly 100 are known in Mammoth Cave. Mammoth Dome, the largest, consists of several domes close together with the partitions broken down to such an extent that a cavity of irregular outline exists, about 400 feet long, 150 feet in maximum width, and 192 feet high. Pits and domes are formed in the same manner and the terms are interchangeable according to the elevation of the observer who views them. Pits (or domes) are openings which extend vertically downward (or upward) through the layers of rock. The process of their formation may be explained as follows: Rain water collects on the surface in sinks and flows through underground passages until it finds a joint or vertical break in the rock, then a waterfall develops. These falls, through solution and abrasion, enlarge the joint or crack into a pit (or dome).

When Green River deepened its valley many of the old underground channels were drained of their waters and stream erosion along these channels ceased. Solution by underground waters was retarded greatly or stopped altogether. In some parts of the upper chambers the deposition of travertine (calcium carbonate) commenced. Such deposits are found to day in the greatest abundance in the higher levels of the Cave, relatively close to the surface. The process of formation of these travertine deposits may be described in brief: After calcium carbonate is dissolved from the overlying limestone by percolating ground water, it is carried in solution downward through crevices and joints until the underground cavity is reached. The air of the cave evaporates the water and provokes the escape of carbon dioxide from it, thus compelling it to deposit its load of calcium carbonate. Travertine deposits vary greatly in size, shape, form, color and abundance, depending on the conditions, both physical and chemical, which prevailed at the time and the place deposition was made. The most common of the many types of travertine deposits are stalactites, which resemble icicles and hang from the ceilings, stalagmites, which build upward from the floors, and flowstone, which covers the walls and floors.

The newly-discovered, yet only partly explored, section of Mammoth Cave contains a profusion of these travertine deposits. Stalactites, snow white in color, have been found by the hundreds along the ceilings of certain passages. The less common branchlike stalactitic forms, helictites, have developed in one location. Stalagmites have been found, and in a side passage off the main avenue a stalactite and a stalagmite have united to form a peculiarly-shaped column, approximately seven and one-half feet high.

If the ground water which enters the cave carries calcium sulphate in solution, the resultant deposit is gypsum. Such deposits include crystalline and fibrous gypsum, incrustations of gypsum, and curious curved forms, often grouped in rosettes, etc. A portion of the recently discovered section of Mammoth Cave is adorned abundantly with these flower-like masses. For several hundred feet in one passageway the rosettes completely cover the walls, ceiling and floor. These decorations are more lavish and spectacular than any heretofore found. Many of the flowers have a diameter of 14 inches, while the petals of some protrude ten inches or more.

Boats on Echo River, One of the Underground Streams in Mammoth Cave National Park, Which Flows 360 Below the Surface.

The arched ceiling of Snowball Dining Room is decorated beautifully with incrustations of gypsum, so protruding in spherical masses as to resemble snowballs. In this room, which is a portion of one of the abandoned stream channels, 267 feet below the surface, a chicken dinner is served daily (for those taking the all-day cave trip), and drinking water is obtained from the "Upside-down Well," cartooned by Robert Ripley. This well was drilled from the surface into a small side passage adjoining the main corridor in which the dining room is located. By means of a novel system of packers and pipes it is arranged so that the water can be taken from the bottom of the well by the force of gravity. Surface telephone and power wires lead through the well into this portion of the Cave.

The "historic" part of Mammoth Cave contains much of interest to the historian and archeologist. Evidence of prehistoric man's occupation is registered unmistakably in certain portions of the second and third levels. But the newly found section shows no trace of its ever having been entered before its discovery a few weeks ago. The avenues in their entirety are in the natural state.

*Butts, Charles: "Mississippian Series in Western Kentucky." Ky. Geol. Survey, 1917.

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Date: 04-Jul-2002