Cave Regions of the Ozarks and Black Hills. Luella Agnes Owen
of magnesia, nitrate of lime, and occasionally sulphate of soda. The tendency which some calcareous rocks have to produce nitrate of lime is, probably, one of the greatest causes of disintegration.'"
"Most extensive subterranean areas thus have been excavated or undermined in Edmonson, Hart, Grayson, Butler, Logan, Todd, Christian and Trig. In the vicinity of Green River, in the first of these counties, the known avenues of the Mammoth Cave amount to two hundred and twenty-three, the united length of the whole being estimated, by those best acquainted with the Cave, at one hundred and fifty miles; say that the average width and height of these passages amount to seven yards each way, which is perhaps near the truth; this would give upwards of twelve million cubic yards of cavernous space which has been excavated through the agency of calcareous waters and atmospheric vicissitudes."
Page 169: "On the south side of Green River the platform of limestone forming the descent into Mammoth Cave is two hundred and thirty-two feet above Green River."
"The entrance to the cave, being thirty-eight feet lower than this bed of limestone, is one hundred and ninety-four feet above Green River. In the above two hundred and thirty-two feet there are several heavy masses of sandstone, viz.: at one hundred and twenty-five, one hundred and forty-five, one hundred and fifty, one hundred and sixty and two hundred and fifteen feet, but it is probable that most of these have tumbled from higher positions in the hill, as no alterations of sandstone have been observed at these levels in the cave. From an elevation of from two hundred and forty to two hundred and fifty feet, the prevalent rock is sandstone without pebbles, which can be seen extending up to three hundred and twelve feet to the foundation of the Cave Hotel. The united thickness of the limestone beds on this part of Green River, is about two hundred and thirty feet, capped with eighty feet of sandstone. About midway of the section on this part of Green River, are limestones of an obscure oolitic structure, but no true oolite was observed. Many of these limestones are of such composition as to be acted on freely by the elements of the atmosphere, which, in the form of nitric acid, combine with the earthy and alkaline bases of calcareous rock, and give rise to the formation of nitrates with the liberation of carbonic acid; hence the disintegrated rubbish of the caves yields nitrate of potash after being treated with the ley of ashes and subsequent evaporation of the saline lixivium. The wonderfully cavernous character of the subcarboniferous limestones of the Green River valley, and, indeed, of these particular members of the subcarboniferous group throughout a great part of its range in Kentucky and Indiana, is due in a great measure to this cause, together with the solvent and eroding effects of water charged with carbonic acid. The 'rock-houses' frequently encountered both in this formation and in the limestones of Silurian date, are produced by similar causes; the more easily disintegrated beds gradually crumbling away, while the more durable remain in overhanging ledges. By the oxidation of other elements, sulphates of oxide of iron and alkalies result, which, by double decomposition, with carbonate of lime, give rise to the formation of gypsums which appears in the form of rosettes, festoons and various other imitative forms on the walls and ceilings of the caves. Crystallizations of sulphate of soda and sulphate of magnesia are not uncommon, both in some of the caves and in sheltered situations under shelving rocks."
The explanations thus given of the excavation and subsequent refilling and decoration of the limestone caves of Kentucky and Indiana apply equally well to those of other states; but it is to be remembered that at the time of Dr. Owen's report, onyx, the most beautiful and valuable of dripstones, had not yet been discovered in the United States; while now especially fine deposits are known in California, Utah, Missouri, South Dakota and Arkansas; the Missouri supply being exceptionally valuable on account of the marvelous delicacy and beauty of its coloring; nor can it soon be exhausted, as deposits have been found in eight counties and further exploration will no doubt discover more.
Concerning the Subcarboniferous, or Mississippian Series in Part I., Vol. IV., Missouri Geological Survey, Dr. C. R. Keyes says: "In the great interior basin of the Mississippi the basal series is exposed more or less continuously over broad areas, extending from northern Iowa to Alabama, and from Ohio to Mexico."
While this broadly extended series of limestone is honey-combed in many places and all directions by wonderful caverns, those of the Ozark regions in Missouri, although comparatively little known, are well worth knowing, and are possibly the most ancient limestone caves in the world. Of the region in which they occur, Dr. Keyes, in the volume last quoted, says: "The chief typographical feature of the state has long been known in the Ozark uplift, a broad plateau with gentle quaquaversal slopes rising to a height of more than one thousand five hundred feet above mean tide, and extending almost entirely across the southern part of the district. On all sides the borders of this highland area are deeply grooved by numberless streams flowing in narrow gorges. Against its nucleus of very ancient granites and porphyries the Ozark series of magnesian limestone was laid down. Then the area occupied by these rocks was elevated, and around its margins were deposited successively the other members of the Paleozoic. The Ozark region was thus the first land to appear within the borders of the present state of Missouri." He further says: "Although it has long been known that the Magnesian Limestones are older than the Trenton, and that they lie immediately upon and against the Archæan crystallines unconformably, their exact geological age has always remained unsettled. There seems to be but little doubt, however, that part of the series is equivalent to the Calciferous of other regions. It is also pretty well determined that certain of the lower beds, all below the 'Saccharoidal' Sandstone perhaps, are representatives of the Upper Cambrian or Potsdam. These conclusions appear well grounded both upon stratigraphical and faunal evidence. The rocks of the Ozark region have not as yet received the necessary detailed study to enable the several lines of demarkation to be drawn with certainty. This investigation is now being carried on as rapidly as possible, and promises very satisfactory and interesting results in the near future."
"The early geological reports represent the Magnesian Limestone series as made up of seven members. Following Swallow, these may be briefly described in the present connection. Beginning at the top, they are:
First Magnesian Limestone.
First, or Saccharoidal Sandstone.
Second Magnesian Limestone.
Second Sandstone.
Third Magnesian Limestone.
Third Sandstone.
Fourth Limestone."
"The Fourth" Magnesian Limestone, or lowest number of the Ozark series recognized, has its typical exposures along the Niangua and Osage rivers in Morgan and Camden counties.
Professor Swallow, in his Missouri Geological Survey Reports I. and II., 1853 and 1854, says: "Caves, natural bridges and subterranean streams occur in the valley of the Osage and its tributaries." The same authority of forty years ago also mentions that "Some of the grandest scenery in the State is produced by the high castellated and mural bluffs of this (Third Magnesian Limestone) Formation, on the Niangua and the Osage." Another reference to the scenery on these rivers describes it as "Wild and grand, beautiful and unique;" with "gaudy-colored bluffs." In the section on building materials he remarks: "One of the most desirable of the Missouri marbles is in the Third Magnesian Limestone on the Niangua. It is fine-grained, crystalline, silico-magnesian limestone of a light drab, slightly tinged with peach-blossom, and beautifully clouded with the same hue or flesh color. It is twenty feet thick and crops out in the bluffs. This marble is rarely surpassed in the qualities which fit it for ornamental architecture."
The Ozarks in the extreme southern portion of the state are even less known to the world, but the scenery is grand, the climate delightful, and the caves worthy of a visit for themselves alone. The State of Missouri being one third larger than England, and of equal size to Switzerland, Holland, Belgium and Denmark combined, it is not surprising that interesting discoveries are still to be expected.
The climate is so varied on account of the range in latitude and altitude, and the natural resources are so great, the claim has been made that if the State were surrounded by an impassable wall, its citizens need not be deprived of any article necessary to a refined and luxurious mode of living: and according to Mr. Henry Gannett in "The Building of a Nation," the population in 1890 was 73.42 per cent. native whites of native parents, the colored a little less than 6