The chief feature in the topography of Ohio is the watershed, which extends across the State from north-east to south-west, and divides its surface into two unequal slopes, the northern, which is much the smaller, sending its waters into Lake Erie and the Gulf of St Lawrence, while the drainage of the other is to the Gulf of Mexico by the Ohio river. The average height of the ridge is about 1100 feet, but it is cut by several gaps, in which the elevation is reduced to about 950 feet. The relief of the State is chiefly due to erosive agencies. The entire drainage area of such a river as, for example, the Muskingum or the Scioto, may be conceived as originally a plain, all portions of which were at approximately the same elevation above the sea. Across this area one main furrow has been drawn, deepening and widening as it advances, and a countless number of narrower and shallower valleys are tributary to it. Fragments of the old plain still remain in the isolated “hills” or tablelands that bound the valleys, and which, though often separated by intervals of miles, still answer to each other with perfect correspondence of altitude and stratification. They rise to a maximum height of 600 feet above the river-channels in the main valleys.

Geology.— The rocky floor is entirely composed of unaltered stratified rocks of Palaeozoic age. Not a single trap dyke or volcanic vent intersects them, and not a trace of igneous metamorphism is shown in any portion of their extent. These strata are disposed in plains so nearly horizontal that the dip is nowhere heavy enough to be safely determined by a clinometer. Not only are sharp flexures wanting, but faults deserving the name are found in but a single corner of a single county. A few low folds, one of which is of preponderating importance, traverse the State and redeem its surface from geological monotony. The only structural irregularity is an occasional case of overlap, but even this is seldom of such a character as to interfere with the easy reading of the record. The aggregate thickness of the entire series will reach 5000 feet if the maximum of each stratum is taken into the account, but if the average measurements are used the thickness does not exceed 3500 feet. The main elements of the scale, which extends from the Lower Silurian (upper portion) to the Upper Coal-measures inclusive, are given below, and the geological sketch-map shows how the surface of the State is distributed among the principal formations. [table]

The Cincinnati group, which constitutes the surface rock for about 4000 square miles in the south-western corner of the State, consists of alternating layers of blue limestone and calcareous shale, both of which contain great numbers of admirably-preserved fossils. The group is undoubtedly equivalent in part to the Hudson River group of the general scale, and by some geologists the name is counted a synonym, but it has not been proved that the Lower Silurian deposits of south-western Ohio can be definitely correlated with the subdivisions of the series in New York. The formation everywhere yields a cheap and excellent supply of building stone, which is also burned into a dark lime, valued for its hydraulic properties. The shales contain notable quantities of alkalis and phosphates, and the soils into which they very readily weather are proverbial for their fertility. The water-supply of the formation is poor, or rather wanting, the impervious shales refusing admission to the rainfall.

The Cincinnati axis, a low fold which traverses the State from south-west to north-east, constitutes its most influential geological feature. It entered Ohio from Kentucky at the close of Lower Silurian time, and gradually extended itself to the northward, until it had converted the western half of the State into dry land. It has left a clear record of its successive stages in the strata which compose it. It did not advance steadily and equally, and the occasional relapses which it experienced have given rise to cases of overlap. It has a low, flat summit, and, on account of the soluble and easily-eroded materials of which it consists, it has suffered more from denuding agencies than the Upper Silurian strata that enclose it, and consequently is now cut down to a lower level than they. In other words, the axis has been converted into a basin.

The Clinton Limestone generally rises in a terrace-like outcrop around the margin of the eroded Cincinnati beds, and its base is marked by the finest line of springs in the State. In its most characteristic phases it is a crystalline limestone that takes a good polish. In very many localities it yields small quantities of petroleum, which seems to be indigenous. The supply is too limited to be valuable.

The Niagara group, also of Upper Silurian age, is of much greater thickness and of proportionally greater economic and scientific importance than the Clinton limestone. As at the Falls, it here consists of a stratum of shale overlain by a massive limestone. It forms the surface rock for about 3000 square miles, but through much of this area it is concealed by heavy beds of Glacial Drift, by which its importance as a factor in the topography and the economic geology of the district is much reduced. In composition the limestone is almost a typical dolomite, but it is still fossiliferous, the fossils occurring as internal casts. It contains a large and interesting fauna. From near the base of the Niagara beds the “Dayton” stone, one of the most valuable building stones of the State, is derived. The formation yields excellent building stones at other horizons also, and its upper beds furnish lime.

The Lower Helderberg Limestone occupies even a wider area as a surface formation than the last-named, but is largely covered with Drift deposits. There are whole counties of which it is known to constitute the rocky floor, in λvhich it does not once rise to the surface. It is seen to the best advantage in the north of Highland county, where it yields a remarkably even - bedded building stone. Like the Niagara Limestone, it is a dolomite in composition. It is poor in fossils, but the few that it contains are highly characteristic.

The transition from Upper Silurian to Devonian time which is made in ascending to the next stratum in the scale, the Corniferous Limestone, is accomplished without any structural break or irregularity, but there is an abrupt lithological change, the latter stratum being a true carbonate of lime, and an abundant and pronounced Devonian fauna appears in its very lowest beds. The Corniferous Limestone forms a narrow belt on each side of the axis, from central Ohio northward, but by the overlap of the next succeeding formations it is entirely lost in southern Ohio. Even where it constitutes the highest bedded rock it is largely obscured by Drift deposits. At Kelly’s Island, Sandusky, Marion, Delaware, and Columbus it is largely worked for building stone, lime, and furnace flux. The earliest vertebrate remains of the Ohio scale are found in this stratum. The box-like skull of a large ganoid fish, Macropetalichthys sulliυanti, Newberry, occurs near the base of the series, and the teeth and bones of other ganoids and selachians are frequently met with in the higher beds. In the State quarries at Columbus these remains constitute a veritable bone bed, a layer 4 to 6 inches in thickness being in large part composed of them.

A heavy deposit of black shale, the Ohio Shale of the table, and the Huron shale of Newberry, directly overlies the Corniferous Limestone in northern and central Ohio, and extends across the State from north to south. It is composed of two black shales, the Cleveland and the Huron, including a blue shale, the Erie, between them. The latter is 1200 feet thick in north-eastern Ohio, but rapidly wedges out as it is followed westward to the axis, and the Cleveland and Huron seem here to be welded into one mass. The black shale contains an average of 8 or 10 per cent, of bituminous matter, a chief source of which is found in a resinous disk of microscopic size that exists in the shale in immense numbers, which Dawson has named Sporangites huronensis. Apart from this minute form the shale is almost barren of fossils, but a few have been discovered in it, mostly at the centres of the great concretions which it contains. The gigantic placoderm, Dinichthys herzcri, Newberry, was first found in these concretions. Though dating back almost to the first appearance of fishes, Newberry has shown that its nearest relationship is with the Lepidosiren of the present day, which zoologists unite in counting as the highest of the entire class. The shale is undoubtedly the source of the natural gas and petroleum of north-eastern Ohio.

The Waverly group, which occupies about 7000 square miles of the surface of the State, is in all respects an important formation. It consists of the Bedford shale, the Berea grit, the Berea shale, the Cuyahoga shale, and the Logan group. The Berea grit has unusual geological interest. Its outcrop is a shore-line across the entire State, and it marks with perfect distinctness the eastern limit of the Cincinnati axis at this date. It is everywhere a quarry stone. The Berea stone and the Amherst stone of northern Ohio and the original Waverly stone of the lower Scioto valley belong to this horizon. In strength, durability, beauty, and the economy with which they can be worked, they stand at the head of the building stones of the State, the value of the annual products of these quarries exceeding $1,000,000. The stone is distributed as far east as the seaboard, and as far west as Duluth. Some of it has even found market in England. The Berea grit is the reservoir of the gas and oil distilled from the underlying shales, and it is also the great source of salt water for Ohio. Another building stone of great excellence and beauty comes from the base of the Cuyahoga shale in southern Ohio,—the Buena Vista stone of the Ohio valley.

The Carboniferous Conglomerate and the Coal-measures have an aggregate thickness of at least 1500 feet, and cover more than 10,000 square miles of the surface of Ohio. The beds of coal, ironore, fire-clay, limestone, and cement rock that they contain render insignificant the contributions made by all other formations to the mineral wealth of the State. The Lower Coal-measures, which are here made to include the Conglomerate group of coals of Pennsylvania, contain the seams of coal enumerated below, which are distributed through 500 to 800 feet of strata. The names of the seams that are used in the Pennsylvania scale are adopted here. [table]

All these coals belong to the bituminous division. Thus far they are almost entirely worked in level free mines, and very little is taken from seams less than 3 feet in general thickness. The average thickness in·the important fields is 5 feet, and the maximum (a small area of a single district) 13 feet. All of the seams enumerated above are worked, but they have very unequal values. The Middle Kittanning seam is by far the first. The Upper Freeport ranks next in value. The Sharon coal is the most valuable in proportion to its area, furnishing, in fact, the standard of comparison for the open-burning coals of the entire Alleghany field. Both it and the Middle Kittanning seam are used in the raw state in the manufacture of iron, a fact which sufficiently attests their purity and general excellence. In the remaining divisions of the Coal-measures there are 10 or 12 additional seams that are of workable thickness at some of the localities in which they occur, but, with one notable exception, these seams are less steady and reliable than those of the lower measures. The exception is the Pittsburg coal, which is, all things considered, the most important seam of the entire coal-field to which it belongs. It is especially valued as a gas coal, and for the production of steam. Its northern outcrop passes through nine counties, with an approximate length of 175 miles, not counting the sinuosities. The area commonly assigned to it in Ohio exceeds 3000 square miles, but the seam has been proved for only a small fraction of the area claimed. In the production of bituminous coal in the United States Ohio ranked third in 1880, the output for that year being about 6,000,000 tons, but the production is rapidly increasing, and the State inspector of mines reckoned the output in 1882 at 8,000,000 tons.

Iron ore is worked at many horizons in the Coal-measures, in seams ranging from 6 inches to 19 feet in thickness. The charcoal iron of the Hanging Rock district of southern Ohio is chiefly applied to the highest uses, as the manufacture of car-wheels and castings for agricultural and other machinery. Of the 99 furnace-stacks that now stand in Ohio, almost all depend in part, and about half depend entirely, on native ore. The amount mined annually exceeds 500,000 tons. In iron and steel industries Ohio ranks next to Pennsylvania, the value of the annual product being $35,000,000. The clays of the Coal-measures are the basis of a large and rapidly growing manufacture of stone and earthen ware. Ohio now produces one-third of the total product of the. United States. In connexion with the salt production, which is large, about half of the bromine of the world is produced in Ohio. The brine of the Tuscarawas valley yields nearly I lb of bromine to 1 barrel of salt.

Three-fourths of Ohio are covered with the various deposits of the Drift period, which consists of “till” or boulder clay, and of the stratified sands and clays of the later stages of the period. These deposits sometimes have a thickness of 300 feet,—their average in north-western Ohio being not less than 50, and in central Ohio not less than 25 feet. In the regions which they cover they exercise a controlling influence upon the relief, drainage, soils, and water-supply. They have filled the valleys of earlier drainage systems, and in many cases have obliterated all traces of their existence. The till is filled with boulders of northern origin derived from the highlands of Canada and from intervening districts. Blocks of large size are sometimes found, some of them showing 2000 cubic feet above ground. In many instances they can be referred by their mineralogical characters to particular localities, or even to particular ledges, from a score of miles to 400 miles distant. The stratified Drift contains vast accumulations of sand, gravel, and clay, all of great economic value. Brick clays of good quality are everywhere accessible. The terminal moraine that forms the boundary of the Glacial deposits is not in all cases as conspicuous as in the States to the east of Ohio, but even where it is least distinct soil and vegetation unite to mark the limit of glacial advance very plainly. The moraine passes through the counties of Columbiana, Stark, Wayne, Richland, Holmes, Licking, Fairfield, Ross, Highland, Adams, and Brown, as recently determined by Professor G. F. Wright.

Soils, Forests.— The division of the State into a drift-covered and driftless region coincides with the most important division of the soils. Below the line of the terminal moraine these are “native,” or, in other words, they are derived from the rocks that underlie them, or that rise above them in the boundaries of the valleys and uplands. They consequently share the varying constitution of these rocks, and are characterized by considerable inequality and by abrupt changes. All are fairly productive, and some, especially those derived from the abundant and easily-soluble limestones of the Upper Coal-measures, are not surpassed in fertility by any soils of the State. Large tracts of these excellent native soils are found in Belmont, Monroe, Noble, and Morgan counties. Among the thinner and less productive soils, which occupy but a small area, are those derived from the Devonian shales. They are, however, well adapted to forest and fruit production. The chestnut and the chestnut oak, both valuable timber trees, are partial to them, and vineyards and orchards thrive remarkably. The native soils of the Waverly group and of the Lower Coal-measures agree in general characters. They are especially adapted to forest growth, reaching the highest standard in quality of timber product. When these lands are brought under the exhaustive tillage that has mainly prevailed in Ohio thus far, they do not hold out well, but the farmer who raises cattle and sheep, keeps to a rotation between grass and small grains, and does not neglect fruit can do well upon them. The cheap lands of Ohio are found in this belt. The other great division of the soils of Ohio—viz., the Drift soils—are by far the most important, alike from their greater area and their intrinsic excellence. Formed by the commingling of the Glacial waste of all the formations to the north of them, over which the ice has passed, they always possess considerable variety of composition, but still in many cases they are strongly coloured by the formation underneath them. When any stratum of uniform composition has a broad outcrop across the line of Glacial advance, the Drift beds that cover its southern portions will be found to have been derived in large part from the formation itself, and will thus resemble native or sedentary soils. Western Ohio is underlain with Silurian limestones, and the Drift is consequently limestone Drift. The soil is so thoroughly that of limestone land that tobacco, a crop which rarely leaves native limestone soils, is grown successfully in several counties of western Ohio, 100 miles or more north of the terminal moraine. The native forests of the Drift regions were, without exception, hard-wood forests, the leading species being oaks, maples, hickories, the walnut, beech, and elm. The walnut, sugar maple, and white hickory are limited to warm, well-drained limestone land; the white oak characterizes the upland clays, while the red maple, the elm, and several of the oaks stand for the regions of sluggish drainage. This noble growth is rapidly disappearing, but several million acres still remain.

Climate.— There is a difference of at least 40° Fahr, between the average summer and winter temperatures. A central east-and-west belt of the State is bounded by the annual isotherms of 51° and 52°, the average winter temperature being 30° and the average summer temperature 73°. Southern Ohio has a mean annual temperature of 54°, and northern Ohio 49°. The annual range is not less than 100°, and sometimes 130°, the extreme of summer heat reaching 100° in the shade, while “cold waves” in winter may depress the mercury to 30° below zero. Extreme changes are liable to occur in the course of a few hours, especially in winter, when the return trades are violently displaced by north-west winds. In such cases the temperature sometimes falls 60° Fahr, in twenty-four hours; changes of 20° or 30° in a day are not unusual. Still the climate proves itself excellently adapted to the finer growths of vegetation, while its effects on human life and on the domestic animals favour a symmetrical development and a high degree of vigour. The rainfall varies between an average of 46 inches in the Ohio valley and an average of 32 inches on the shore of Lake Erie (spring 10 to 12 inches, summer 10 to 14 inches, autumn 8...