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 Alleghenies 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 colitic structure. In it are found valuable beds of iron ore, some zinc and lead ores, and large veins of fluorspar. 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 Western 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.
Todd County, it will be observed, is geologically placed very high. The rock exposures belong entirely to the fifth and sixth formations of the State section, which brings the county within the region of the Western Coal Field. It lies, however, on the margin of this area and no important outcrops of coal have been worked to any great extent. One or two mines have been opened and the product sold to local consumers, but with no great pecuniary profit. There is but little known of the deposits of this mineral in Todd, the State survey having accomplished but little more than to demonstrate what was generally known before, that there was coal here to some indefinite extent. An attempt was made in 1859 under the guidance of the State Geologist, Mr. D. D. Owen, to trace the margin of the Western Coal Field. The work of the season began on the Ohio River, at Stephensport, Breckinridge County, extending into Breckinridge, Grayson, Edmonson, Hart, Warren, Butler, Logan, Todd, Christian, Muhlenburg, Hopkins, Ohio and Hancock Counties. The greater part of the region traversed was the roughest country in western ‘Kentucky. The margin of this coal field is surrounded by the millstone grit, sandstones and the intercalated beds’ of limestone and aluminous shales; usually dipping at a considerable angle. These formations worn into deep ravines by most of the water-courses produce a broken country, while the interval between the streams is usually filled with steep, rocky hills. This is the character of northern Todd, and it is probable that no mines will ever be discovered here which will prove of considerable commercial advantage. The geological party approached Todd by way of the Greenville road. Several patches or outliers of coal measures were seen on the hills between the northern branches of Muddy River and Clifty Creek, rarely over sixty or seventy feet thick above the fifth sandstone of the general section. Near the crossing of Clifty Creek the fifth sandstone is seen in heavy masses twenty-five or thirty feet thick. North of Clifty the coal measures are reached at the Dughill, half a mile southeast of the Rochester and Elkton road. From this point to the “Narrows” the road lies about 150 feet above the fifth sandstone; near the Narrows the road suddenly descends to the fifth sandstone, i. e., the margin of the coal measures. The fifth sandstone dips to both sides of the road from the ridge (Narrows), which is probably an anticlinal wave; the synclinals on either side being in the beds of Clifty Creek on the east, and eastern branches of Pond River on the west side of the ridge. South of the Narrows the fourth limestone and the fourth sandstone dip rapidly toward the northeast, and are raised a considerable distance above the horizontal position of the fifth sandstone at the Narrows. The narrow part of the ridge is about sixty yards wide, being in fact only a huge mass of the fifth sandstone, eighty feet thick, which is little else than a loose mass of quartz pebbles about the size of marbles, through which the water percolates. Being arrested by the clay shales at the base of the sandstone, it breaks out in bold springs on the east side of the ridge, which is doubtless the direction of the greatest dip of this locality. About one mile south of the Narrows the road has descended to the third sandstone, and the rocks are quite level or are dipping gently to the southwest, with the line of the branches to Pond River. The coal measures lying between the head of Pond River and Clifty are only a few feet thick-80 to 110-from one to two miles wide, deeply indented by the streams especially on the west or Pond River side of the ridge. From the point of intersection of the ” Old Highland Lick ” road with the Elkton and Greenville road the line of survey turned to the westward to Bennett’s Mill, White Plains and on to Christian County. At this point of deflection, sandstone No. 3, formed the surface rock, and on descending the first hill limestone No. 2 was reached. Near the East Fork of Pond River the dip becomes quite rapid and brings down the mass of limestone No. 3 with its associated shale beds to the East Fork, in a few places covered by fallen masses of the pebbly part of the fifth sand-stone.
The line dividing the exposures of the fifth and sixth formations, the cavernous limestone and the grit sandstone or free-stone, is nearly coincident with the Russellville and Hopkinsville road. In the former are found several beds of limestone, differing much in thickness and quality, which commend themselves for building purposes. The best of these is that used by the company quarrying near Bowling Green. It is an oolitic, magnesian limestone, occurring in layers of excellent form for use, readily worked, and with rare qualities of endurance. A very similar stone is found in Todd, which was used in the foundation of the court house built in 1835, and on which the tool marks can be quite distinctly traced at this day. When first taken from the bed the stone is rather soft, so that it can be carved with some facility, but when it is long exposed it acquires a much greater hardness. It is, for a limestone, very resistant to heat, and is likely to wear better than any other stone in the Mississippi Valley. Add to this a rare beauty of color, a cream tint, and an endurance of this color, and all the desirable qualities of a building stone are well represented. This stone may be sought about one hundred and fifty feet below the top of the main carboniferous limestone. The lithographic limestones which are found at a lower point in the carboniferous limestone series, are as yet less determined in their value than the building stones. The conditions which determine the goodness of this quality of stone are so many, and must be met with such accuracy, that it is by no means certain that there is any material here to satisfy these conditions. The extensive series of beds which lead to the hope that the stone of this county may be suitable for this purpose, were formed under the same general conditions as prevailed in the basin when the most trusted lithographic stone, that of Solenhofen, are found ;-a sea bottom, whereon an unbroken mass of fine sediment of mingled lime and clay is accumulating, an entire absence of animals large enough for the naked eye to see-these seem to be the conditions under which a lithographic stone must be formed. Unfortunately most of this stone here shows from point to point small hard bits, which are probably the remains of some silicious sponge which lived in these waters of the ancient sea. These stones are doubtless useful for the making of the coarser sorts of engraving and the ordinary run of crayon work. They may also prove suitable for ordinary transfer work. None have been found as yet suitable for the highest grades of work.