divisions here recognized are called the Galena and the Trenton limestone. They are, respectively, 250 and 100 feet thick in maximum measurements. The upper, or Galena division, is, in its best state, a light-colored blue or drab, coarse-grained, porous, and almost pure dolomite. The underlying Trenton is, also, generally magnesian in com position, but it does not quite reach dolomitic proportions. It is also less pure in the main than the best phases of the Galena. (Geol. of Wisc., Vol. I.) In central Kentucky, again, a twofold division of the Trenton is recognized, the two members being known as the Trenton and Birdseye divisions. The former is reported to be 175 feet in thickness, and the latter 130 feet. (Rocks of Central Kentucky, W. M. Linney, Ky. Geol. Survey, 1882.) In composition, the Trenton of Kentucky is impure, and contains but a small percentage (five to ten) of carbonate of magnesia, so far as can be judged from the few analyses available. In Ohio, the Trenton limestone appears to agree in its divisions with those of Wisconsin on one side and with those of Kentucky on the other. In other words, it has a threefold division when all the deposits of this age in the state with which we have become acquainted are taken into account. In southern Ohio, the Kentucky series appears in the well sections, consisting of the Trenton proper and the underlying Birdseye. In northwestern Ohio, we find in the new oil and gas-rock, a stratum which is, so far as composition goes, the equivalent of the Galena dolomite, underneath which, rocks having the composition of the Trenton and Birdseye of the south appear. The position of the Galena limestone in the geological scale, it must be added, is not entirely settled. A question has, at least, been raised in regard to it. Mr. C. D. Walcott, of the United States Geological Survey, has urged the view that instead of belonging to the Trenton epoch, it is really the equivalent and representative of the Utica shale, no trace of which in its characteristic form is found in the Wisconsin section. The absence of the shale proper is, in fact, one of the strongest arguments brought forward for the new reference. If the oil-rock of Ohio represents the Galena dolomite, then the argument above-named loses its force, because over this formation there is found the full section of the Utica shale, normal in every particular. If it does not represent the Galena division, it still exhibits as marked a departure from the ordinary character of the Trenton limestone as the latter does, and thus weakens the argument for separating the Galena. A number of analyses of the several members of the Trenton group will here be given, illustrative of the differences in composition that have been already referred to. The uppermost, or dolomite division, will be represented first: 6. Upper beds of Trenton limestone, Escanaba river, Michigan. -Geol. Survey. The next group of analyses represents the composition of a lower division of the Trenton series, which is counted the Trenton limestone proper in a considerable part of the country. Under this head the Trenton of New York and New Jersey will find a place. No sharp line can be drawn between this and the succeeding group: No. 1-Drillings 100 feet below gas-rock, Bowling Green, Ohio.-Lord. 50 feet below surface of Trenton, Springfield, Ohio.-Lord. No. 2- No. 4 Whitefish Another group of analyses represents the composition of the uppermost beds of the Trenton limestone at various points in Ohio outside of the productive oil and gas-fields. This group will include the Trenton limestone of central Kentucky as well: This group blends and crosses with group No. 2. The same rock, doubtless, appears in both tables. A fourth group is, however, added, in which the proportions of lime and magnesia are seen to be a mean between the first and second tables. The geographical locations of the points here named must be observed. They belong on the edge of the productive fields. Nos. 6 and 7 of the preceding table might, with equal propriety, find a place here. No. 1-Top of Trenton limestone at Fostoria.-Lord. Still another variety of composition is found in the Trenton limestone of Ohio, and also of other adjacent states. This stratum is sometimes, though rarely, a nearly pure carbonate of lime. This phase is shown in the gas-rock of St. Henry's, Mercer county, Ohio, and also in the glass-rock, so-called, of Wisconsin. The Trenton limestone of Carey and Dunkirk, Ohio, will probably be found to agree with the St. Henry's rock. Many other analyses will be added and discussed in the body of the chapter, and after the facts of gas and oil production have been stated, the connection existing between the chemical and petroliferous characters of the rock will be considered. It is already apparent that two very distinct types of rock are now grouped in Ohio under the name of Trenton limestone, and that all the valuable qualities of the one are popularly, but vainly, expected from the other also. In New York and Canada, the Trenton limestone is directly overlain by the Utica shale, a stratum of brown or black, fine-grained shale, poor in fossils, as a rule, but containing a few which are strictly characteristic, that is, that are found nowhere else. The Utica shale ranges between 200 and 300 feet in thickness in its typical localities in New York. Above this well-marked deposit, in the eastern territory already named, another stratum of shale, sometimes interstratified with thin courses of limestone, is found. It is named the Hudson River shale. It has a maximum thickness in New York of 1,000 feet, and an average thickness of perhaps half this measure to the westward, where it becomes more calcareous. It is mainly light-blue, or greenish-blue in color, and contains many fossils. Above the Hudson River shales is the Medina formation, red sandstone at the eastward, and red shale at the west. Its color is characteristic, as there is no similar element in this part of the scale. The Hudson River and Utica shales, when followed to southern Ohio, seem to have lost their distinguishing lithological characteristics, and to be blended in a common mass of blue calcareous shale, with many thin layers of interstratified limestone, both limestone and shale being highly fossiliferous. To this blended stratum the name Cincinnati group is given. The Trenton limestone, as already shown, rises to the surface at but a single point within the limit of the state (page 5). Its nearest important outcrops are in the Blue Grass region of central Kentucky, and in the Manitoulin Islands, north of Lake Huron. In the valley of the Ohio, at Cincinnati, we are obliged to descend about three hundred feet beneath the surface to reach it. This limestone is known to be a source of petroleum at many localities. Dana says of it, in New York, "it is sometimes bituminous, especially in its upper portions." He speaks of small quantities of oil being contained in it at Watertown, New York, and also at Montmorenci and Pakenham, Canada. Hunt asserts that it contains petroleum in its outcrops in the Manitoulin Islands. He instances one well that produced 120 barrels. In southern Kentucky and in Tennessee, this same limestone has been credited with a part, at least, of the large production of oil that has occurred there. A single well is claimed to have produced 50,000 barrels, but its oil was probably derived from the Hudson River series. Within the last three years, the Trenton limestone has been proved to be a source of high-pressure gas, and of petroleum in considerable quantity at several points in northwestern Ohio, and later in central Indiana. Although this formation was believed to underlie the part of the state in which it has been found, and although it was known to be petroliferous in its nearest outcrops, both north and south, the occurrence of oil and gas in quantity in it in Ohio, had not only not been predicted, but was entirely unexpected. One reason why it was not expected was, that this stratum had been previously reached and penetrated in several deep borings within the state without any sign of the presence of either oil or gas in considerable quantity. The best known of these borings was the deep well in the State House grounds at Columbus. This boring was undertaken to supply the State House with water, and it was carried to a depth of 2,775 feet. Its record is as follows, being quoted from Newberry's account in Geology of Ohio, I, 113 : |