No geological survey has been made of Todd County, and the State work is of such a general nature as to forbid the gathering of anything approaching a particular review of the geological features of this county from its pages. A brief general review is all that can be attempted in the time and space assigned to this topic here. The geological formations of Kentucky, in common with those of the other Western States, generally belong to that great system which extends from the Alleghanies on the east across the Mississippi and to the Rocky Mountains on the west. Throughout this vast region the primary fossiliferous or silurian devonian, and carboniferous rocks prevail with some of the upper formations. These rocks all belong to the class which is termed sedimentary, and were generally deposited upon the bottom of the primeval ocean. Here the fossil remains of the inhabitants of this ocean were gradually covered by clay and sand or limestone and other layers of shells, until, under the heavy pressure of superincumbent strata and by slow and long-continued chemical action, they were converted into solid rocks, and now that the waters of this ocean have retired, are exposed to view as the lasting records of earth’s remotest history. The strata over nearly the entire surface of the State lie nearly horizontal with few dislocations. They have generally a slight dip which, in the lower strata, seems to be usually in every direction from a point near Cincinnati on the Ohio River as a center, and at this point the lowest surface rocks of the State are exposed. The lowest exposed formation is the blue limestone, generally considered equivalent to the lower silurian strata of Murchison. The main surface exposure of this formation is found in a great curved triangular area, the southern apex of which terminates in Lincoln County, and from which only a narrow strip or axis, occasionally to be observed in the deep cuts of the valleys, can be traced through Casey, Russell and Cumberland Counties to the Cumberland River in Monroe County. The second formation is the gray or cliff limestone. The termini of this formation are found on the Ohio River, always overlaying the blue lime-stone, extending from Lewis and Mason Counties above to those of Trimble and Oldham below. From these points this formation appears as a belt, varying from twenty-two miles in width in Jefferson County to only a fraction of a mile where it enters Tennessee from Monroe County, running in a course more or less meandering from its true termini on the Ohio around the blue limestone. Its dip corresponds generally with that of this lower formation. This formation is known also as the cliff lime-stone, because the hardness and durability of some of its layers causes it to stand out in bold cliffs and to be the cause of the falls of water-courses. It is believed that its lower beds are equivalent with the upper silurian strata of Murchison and its upper layers with some portion of his devonian. The third formation is variously termed black lingula shale, black slate, devonian shale. This formation, resting immediately on the second formation, appears also on the Ohio River at two points: in Lewis County and at the base of the falls of that river in Jefferson County. From these two points, where the Ohio River Valley cuts through these strata as they pass to the north and west, this formation like that below it sweeps around the gray limestone in a meandering, irregular belt, varying in breadth from eight to ten miles in parts of Lewis, Bath, Estill and Madison Counties to that of a fraction of a mile in Casey, Russell, Cumber-land and Monroe Counties. Like the second formation it passes into the State of Tennessee near the Turkey Neck Bend of the Cumberland River in two neighboring narrow zones lying on each side of the axis described under the head of the first formation, and its two zones, nearly parallel in their northeasterly course from the Tennessee line to the confines of Lincoln County, begin here to diverge, like those of the second formation, so as to surround and invest that lower formation. Its thickness at the falls of the Ohio is a little over 100 feet, but it varies greatly in this respect. This shale is quite bituminous, and petroleum has been found in this as well as in the formations above and below it. Some search has been made in it for coal but only with disappointment. No workable beds of this mineral have ever been found so low as this in the strata of the earth in America. The fourth formation is knob sandstone. This formation, which is generally characterized by the presence of those low hills called “knobs,” is mainly composed of olive gray shales and grits or sandstones of the same tint. It is calculated to be 350 to 550 feet in thickness, and some of the knobs, as Sweet Lick Knob in Estill County, rise to 500 feet above the level of the streams. This formation also sweeps around the central and lower formations on the outside and above the black shale very much in the same course as described. This formation is exposed in a belt of about fourteen miles wide, extending from the foot of the falls of the Ohio to the mouth of the Salt River; thence it bears up the valley of that stream nearly south, with a slight easterly curve, to Muldraugh’s Hill, dividing Taylor, Marion and Larue Counties, occupying part of Bullitt to the northeastern edge of Hardin, the western corner of Nelson and a large portion of Larue; thence it curves more to the southeast through the corners of Taylor, Casey and Adair Counties, to be continued in the form of low beds of dark earthy limestones and marly shales through Russell and Cumberland Counties to the Tennessee line. Beginning at its upper limits on the Ohio River in Lewis County its trace is found through the northeastern part of Fleming, the northern portion of Rowan, through Bath, Montgomery, Powell, Estill, Madison, Garrard, Boyle and Lincoln, in its southeastern sweep, to Casey County; again to pass, on the other side of the central axis, to the Cumberland River. The fifth formation, known as cavernous limestone, sub-carboniferous limestone or mountain limestone, is the exposure found in the southern portion of Todd. This formation is made up of alternating layers of white, gray, reddish, buff, and sometimes dark gray colored rocks, varying in quality from the most argillaceous claystone to the purest lime-stone. The latter predominates here, however, and contains numerous caverns, of which the Mammoth Cave in Edmonson County is an exaggerated specimen. These caverns are especially marked in Todd County only by the ” sinks ” found here and there in which the drainage water of the country sinks to form underground streams. Clear and copious springs mark the junction of this limestone with the underlying knob-stone, and its lower strata contain in many places the dark, flinty pebbles which furnished the material for the arrowheads of the Indians. Some of its layers are so compact and close textured as to be fit for the lithographer, others are beautifully white with an oolitic structure. In it are found valuable beds of iron ore, some zinc and lead ores, and large veins of fluor-spar. This formation is geologically important as being the basis of the true coal measures, no workable beds of that material having ever been found below this formation in any part of the world. It surrounds the coal fields on all sides, and, like the other lower formations, is believed to extend continuously under them, appearing always in its relative position in the beds of streams or bottoms of valleys which are cut down deeply enough in the coal measures. The principal surface exposure is in the central portion of the State, the counties of Adair, Allen, Barren, Greene, Warren, Logan, Simpson and much of Hart, Edmonson, Todd, Trigg, Christian, Caldwell, Crittenden, Monroe, Butler, Grayson, Ohio, Taylor and Larue being based upon it. The sixth formation, the carboniferous or coal measures, is found in the northern part of Todd. The lower member of this formation, resting on the sub-carboniferous lime-stone, is usually what is called the conglomerate, millstone grit or pudding stone, which is generally composed of quartz pebbles, more or less coarse and rounded, cemented together with a silicious or ferruginous cement, but sometimes represented by fine sandstone or even shaly layers. Where the hard layers of this rock, the millstone grit, prevail the hills are steep, cliffs prominent and the, soil but little productive. The true coal series, based upon this rock, are made up of alternating layers of sandstones, shales, conglomerates and limestones, contain various beds of coal, and nodules and layers of iron ore. Two considerable areas of this formation exist in the State which are termed the Eastern and West-ern Coal Fields. The Western Coal Field is an extension of the Illinois and Indiana coal field, and occupies the whole of Union, Henderson, Daviess and Hopkins, and large portions of Hancock, Ohio, Muhlenburg, Grayson, Todd and Butler Counties, an area of about 3,888 square miles. The seventh formation is composed of the quaternary deposits found in the extreme southwestern counties of the Jackson Purchase, situated between the Tennessee and Mississippi Rivers. These are loams, marls, clays, etc., which have probably been transported there by the action of water in recent geological time.
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