The geological structure of that portion of southern Missouri which lies to the westward of the Archean rocks near the Mississippi River is peculiarly suitable for the development of caverns. The Ozark uplift produced far-reaching undulations, and th ... Read more

The geological structure of that portion of southern Missouri which lies to the westward of the Archean rocks near the Mississippi River is peculiarly suitable for the development of caverns. The Ozark uplift produced far-reaching undulations, and there seem to have been no violent disturbances which would result in extensive faults, considerable displacements, or a pronounced inclination of the strata. Jointing and pressure cleavage, however, gave rise to innumerable crevices in the limestone, through which percolating surface water found its way into all parts of the formations. By its solvent power this water gradually enlarged the crevices into passages which, multiplying and uniting, drained constantly increasing areas until they formed subterranean streams with a perpetual flow. Thus began caverns; and these grew in depth, width, and height as the rock was eroded and dissolved. Tributary crevices were subject to the same action; and there was finally created by each of these water systems a network of cavities whose ramifications sometimes extend throughout several townships. In time, sections of the roof, here and there, became so thin from the combined erosion taking place both above and below as to be unable to sustain their own weight; the overlying strata fell into the cave, and the volume of water flowing through it was augmented by drainage which had previously been disposed of on the surface. All this had to seek an outlet somewhere, except in those rare instances where it maintains its downward course until, below the level of any open stream it can reach, it encounters an impervious stratum and must lose itself in the deep rocks. Usually, however, it emerges in the face of a bluff or on the side of a hill; and the opening becomes "the mouth of a cave." Occasionally, in such situations, the water continues to flow out; but usually it finds a way to reach a lower level, and so the cave in time becomes dry except for such water as seeps through from the earth immediately above. Sometimes, too, the point of discharge is at or perhaps somewhat below the level of a stream into which it passes; in the Ozarks are numerous very large springs or fountains which by inverted siphon or artesian action are forced up from subterranean streams lying at a greater depth. Few large caverns have the floor entirely dry, even when they are well above the bottom of the valley. Deposits in the front portion may be dry, perhaps dusty on the surface; but toward the interior moisture usually accumulates until they are muddy or until the water stands in pools or puddles. When this is the case there is sometimes a little stream making its way to the front through a channel which it has cut; or seepage may dampen, possibly saturate, the lowermost portions of the otherwise dry earth. These details are controlled principally by the direction and degree of slopes and by side openings which allow more or less of the water to escape at some part of its journey. When a cavern is fairly lighted and has a dry floor, whether of rock or earth, it forms an excellent abode for a small community unable or not disposed to construct shelters more comfortable or convenient; and there is abundant evidence that many caves in the Ozarks were utilized as habitations by the aborigines. It must be remembered, however, that in the centuries which have elapsed since hunters or permanent occupants first entered this region, many superficial changes have taken place, not only about the entrances but within the caverns as well. Very probably these alterations have converted caves once occupied into places which at present are quite unfit for such purposes. Talus has accumulated in front of the openings or partially filled the front chambers; it may well be the case that this conceals much refuse. Caves which, from similar deposits, are now difficult to enter and dark to the doorway, may have been open and convenient. Furthermore, caves with wet or muddy bottoms may owe such condition to causes which have recently come into operation; or if they always contained more or less water, the primitive dwellers could in many cases have overcome such disadvantages by digging drains which have since become choked and obliterated. Very small cavities, such as deep rock-shelters; or caverns with a great thickness of earth on the floors, now showing no trace of remains; or those with entrances so small that it is necessary to crawl through—any of these, if cleared out to the bottoms, might disclose material dating back to very early times. Less