produced by the gradual change of the surface configuration.
The geological formation of Clinton county consists mainly of the upper coal measures. A thin strata of coal in this measure, which might be advantageously worked at some points by stripping along their outcrops, and thus supply a limited local demand. The main reliance for a supply of coal, however, must be placed upon the coal of the lower coal measures, which can only be reached at a considerable depth by extensive mining operations. There is no doubt but that the St. Clair county coal extends eastward under the whole surface of Clinton county.
The Upper Sandstone Formation appears to consist in Clinton county mainly of shales, many of which are arenaceous and full of concretions of carbonate of iron, interstratified with thinly-bedded sandstones. This formation, as developed in this county, presents several calcareous intercalations, especially one near its base, and another in- its upper portion. Of these none contain sufficient lime to form a heavy layer of limestone, but form calcareous sandstones, calcareous mudstones, and calcareous slates. In the upper part of the formation a seam of coal has been observed at different points, from ten to twelve inches in thickness. - The upper sandstone formation occupies mainly the eastern part of Clinton county.
The Shoal Creek Limestone is P. light-colored-mostly light-bluish-gray-limestone, with a fracture varying from sub-conchoidal to uneven, and sub-crystalline and compact texture. It sometimes forms layers of eighteen
inches or more in thickness, sometimes thinner ledges, and at most points quarries well, and is finely adapted for building purposes. Its thickness varies between six and eleven feet, and is generally about eight feet. The name Shoal Creek limestone has been given to this bed because it is most prominently exposed in numerous outcrops on Shoal Creek and its vicinity, and we find there no other limestone with which it could be confounded.
Coal underlies the whole of Clinton county, and is the principal mineral product. The depth at which the Belleville coal is reached increases to the eastward. The upper coal seams are thin, and cannot profitably be worked, only for local demands, where it outcrops. Coal is being developed at Centralia, Sandoval and Trenton. The mines will be fully described in the township histories in this work.
Minerals.-Concretions of impure carbonate of iron and kidney ore are sometimes found in the shales of the coal measures. These are nowhere accumulated in sufficient quantity to be valuable as an iron ore.
Building Materials.-As far as the Shoal Creek limestone extends in the northwest and central parts of the county, it furnishes a superior building stone, and, when burnt, a good -but not very white-lime. At a few points sandstone is quarried, and on Crooked Creek the areno-calsareous layers. In the southwestern and northern parts of the county rock are not easily accessible, but good brick can be manufactured anywhere. Timber is also plenty for building and other purposes.