Page:History of Richland County, Ohio.djvu/26

 accurately surveyed, yet Ohio remained a kind of terra ivcognita, of which the geology was less known than any part of the surrounding area.

In 1809, the Legislature appropriated, for a new survey, $13,900 for its support during one year, and appointed Dr. Newberry Chief Geologist; E. B. Andrews, Edward Orton and J. H. Klipplart were appointed Assistants, and T. G. Wormley, Chemist. The result of the first year's work was a volume of 164 pages, octavo, published in 1870.

This report, accompanied by maps and charts, for the first time accurately defined the geological formations as to age and area. Evidence was given which set at rest questions of nearly thirty years' standing, and established the fact that Ohio includes nearly double the number of formations before supposed to exist. Since that date, the surveys have been regularly made. Each county is being surveyed by itself, and its formation accurately determined. Elsewhere in these pages, these results are given, and to them the reader is referred for the specific geology of the county. Only general results can be noted here.

On the general geological map of the State, are two sections of the State, taken at each northern and southern extremity. These show, with the map, the general outline of the geological features of Ohio, and are all that can be given here. Both sections show the general arrangements of the formation, and prove that they lie in sheets resting one upon another, but not horizontally, as a great arch traverses the State from Cincinnati to the lake shore, between Toledo and Sandusky. Along this line, which extends southward to Nashville, Teun., all the rocks are raised in a ridge or fold, once a low mountain chain. In the lapse of ages, it has, however, been extensively worn away, and now, along a large part of its course, the strata which once arched over it are removed from its summit, and are found resting in regular order on either side, dipping away from its axis. Where the ridge was highest, the erosion has been greatest, that being the reason why the oldest rocks are exposed in the region about Cin- cinnati. By following the line of this great arch from Cincinnati northward, it will be seen that the Helderberg limestone (No. 4), midway of the State, is still unbroken, and stretches from side to side; while the Oriskany, the Corniferous, the Hamilton and the Huron formations, though generally removed from the crown of the arch, still remain over a limited area near Bellefontaine, where they form an island, which proves the former continuity of the strata which comprise it.

On the east side of the great anticlinal axis, the rocks dip down into a basin, which, for several hundred miles north and south, occupies the interval between the Nashville and Cincinnati ridge and the first fold of the Alleghany Mountains. In this basin, all the strata form trough-like layers, their edges outcropping eastward on the flanks of the Alleghenies, and westward along the anticlinal axis. As they dip from this margin eastward toward the center of the trough, near its middle, on the eastern border of the State, the older rocks are deeply buried, and the surface is here underlaid by the highest and most recent of our rock formations, the coal measures. In the northwestern corner of the State, the strata dip northwest from the anticlinal and pass under the Michigan coal basin, precisely as the same formations east of the anticlinal dip beneath the Alleghany coal-field, of which Ohio's coal area forms a part.

The rocks underlying the State all belong to three of the great groups which geologists have termed " systems," namely, the Silurian, Devonian and Carboniferous. Each of these are again subdivided, for convenience, and numbered. Thus the Silurian system includes the Cincinnati group, the Medina and Clinton groups, the Niagara group, and the Salina and Water-Line groups. The Devonian system includes the Oriskany sand- stone, the Carboniferous limestone, the Hamilton group, the Huron shale and the Erie shales. The Carboniferous system includes the Waverly group, the Carboniferous Conglomerate, the Coal Measures and the Drift. This last includes the surface, and has been divided into six parts, numbering from the lowest, viz.: A glacialed surface, the Glacial Drift, the Erie Clays, the Forest Bed, the Iceberg Drift and the Terraces or Beaches, which mark intervals of stability in the gradual recession of the water surface to its present level.

"The history we may learn from these formations," says the geologist, " is something as follows :

"First. Subsequent to the Tertiary was a period of continual elevation, during which the topography of the country was much the same as now, the draining streams following the lines they now do, but cutting down their beds until they flowed sometimes two hundred feet lower than they do at present. In the latter part of this period of elevation, glaciers, descending from the Canadian