592 OHIO Helderberg of New York, is very largely de- veloped jn the western part of the state and on the islands of Lake Erie. It flanks both sides of the Cincinnati arch, and its thickness near the lake is about 100 ft. The base of the Devonian system, the Oriskany, is recogniz- able in a few places as a saccharoidal sand- stone, 3 to 10 ft. thick. The corniferous lime- stone, the chief element of the Devonian in Ohio, forms two belts of outcrop on opposite sides of the Cincinnati arch, one extending from Sandusky, where it is about 100 ft. thick, thinning put southward toward Columbus and disappearing in Pickaway co. The other belt crosses the N. W. corner of the state diago- nally from Michigan near Toledo to the Indiana line near Van Wert. The surface rock of Kelley's island is also formed of corniferous limestone. It is largely quarried at Kelley's island, Sandusky, Columbus, and elsewhere for building stone and lime, and the state house at Columbus is built of it. The corniferous at Delaware and Sandusky also yields interesting fossil fish remains, such as macropetalicJithys and onychodus. The Hamilton is exhibited in but few localities as a thin bed of marly lime- stone overlying the corniferous. The Huron or black shale, the equivalent of the Genesee and lower part of the Portage of New York, is a mass of black bituminous shale 300 ft. thick containing 10 to 20 per cent, of carbon- aceous matter. It occupies the entire N. W. corner of the state and a belt 10 to 20 m. wide extending from the mouth of the Huron river on Lake Erie to the Ohio. It contains the re- mains of huge fossil fishes, dinichthys, and is the source of the oil and gas of Pennsylvania and parts of Ohio. The Erie shale, the upper member of the Devonian and the continuation of the Portage and Chemung of western New York, is a mass of argillaceous shale bordering the lake shore from the Pennsylvania line, where it is 1,000 ft. thick, to the Vermilion river, where it has thinned out and disappeared. Nearly the entire E. half of this state is un- derlaid by the members of the carboniferous system, which here form the N. W. border of the great Alleghany coal field. The base of this system is composed of the shales and sand- stones of this Waverley group, which are the western continuation of the " vespertine " of Pennsylvania. The Berea grit, a sandstone stratum of the Waverley, is extensively quar- ried at Berea, Amherst, Independence, &c., in the N. part, and at Buena Vista in the S. part of the state, from which places it is largely exported for building purposes and grindstones. The S. E. third of the state is occupied by the coal measures, which are underlaid at places by the conglomerate, especially in the N. part, where it is locally 175 ft. thick ; and also by the carboniferous limestone, which however is rarely over 20 ft. thick, and does not extend N. of the central part of the state. The coal measures are composed of strata of shale, sand- stone, coal, limestone, and fire clay with iron ores, with a maximum thickness of 1,200 ft. These cover in Ohio an area estimated at 10,- 000 sq. m. They are divided into the lower coal measures, 400 ft. thick, the barren mea- sures, 400 ft., and the upper coal measures, 300 to 600 ft. In the lower coal measures there are seven workable seams of coal of general extent, varying in thickness from 2$- to 13 ft. The lowest and one of the most im- portant seams is coal No. 1, the Brier Hill, Massillon, and Jackson coal. This is an open- burning block coal, 2 to 6 ft. thick, and is used extensively in the iron manufacture in the Mahoning and Tuscarawas valleys, and in Jackson co. Coal No. 6 is one of the most extended and valuable seams in the state. It is of variable thickness, and in the Hocking valley at Straitsville, &c., attains a maximum thickness of 12 to 13 ft. It is generally a co- king coal, but as best developed in, the Hock- ing valley is an excellent open-burning coal. The barren coal measures are so called because of the absence from them of any extended workable coals, though locally seams occur of value. The upper coal measures contain three to four workable seams, the lowest and most important of which is the Pittsburgh coal, or coal No. 8. It occupies the district extend- ing from Steubenville to McConnellsville and Pomeroy. It is a strong caking coal, but in- ferior in quality to the same seam as developed in S. W. Pennsylvania. The deposits of the drift or quaternary cover about two thirds of the area of Ohio, and extend from the lake southward to a line irregularly drawn from the N. line of Columbiana co. on the east to Dayton and the Indiana line on the south- west. They consist of heavy beds of clay (the Erie clay), sand, gravel, and bowlders, attain- ing sometimes a thickness of 200 ft., and giv- ing character to the agriculture of large areas. The underlying rocks are often found planed, scored, and polished by glaciers. An interest- ing feature in the surface geology of Ohio is the buried river channels and deeply excavated troughs, now filled wholly or partially by sand, gravel, &c., many of which are occupied by rivers now flowing far above their old rocky bottoms. This points to a time at which the land was more elevated than at present, during which the river channels were excavated, and to a subsequent period during which the land was less elevated, and the channels were filled up ; and it is considered that the area of the state has never been wholly submerged since the close of the carboniferous age. The prin- cipal mineral products of Ohio are coal, iron, clays, gypsum, peat, salt, petroleum, lime, hy- draulic cement, marl, and building stone. Coal is the great mineral staple of the state. The distribution and quality of the Ohio coals have been already noticed. The iron ores of the lower coal measures in the Hanging Kock region, in Lawrence, Jackson, and Scioto cos., are of great value, and sustain an iron man- ufacture of large extent. Blackband ore is
