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in less than half a mile. Frequently the strata descend at the rate of one foot in eight for 1,000 or 1,200 feet of horizontal distance. The break is equally well defined at Findlay, North Baltimore, Bowling Green, Monclova and Sylvania.

7. In front of this bifurcated axis in northwestern Ohio, and doubtless also in northeastern Indiana, there is a steep and rapid descent of the Trenton limestone as it takes its place under the Michigan coal field. The rocks appear to fall in a due north direction. A synclinal trough of the Trenton is revealed by the wells that have been drilled at Napoleon and Wauseon. The Trenton was found in the first at a depth of 1,114 feet blow tide, and in the second at a depth of 1,367 feet below tide. The latter figure was entirely unexpected, since at Toledo upon one side the level of the Trenton was found to be 800 feet below tide, and at Bryan upon the other side, 1,240 feet below, and no indication was apparent of any irregularity in the interval.

8. The contour lines in the northeastern section of the map follow meridians, as will be seen, that is, they are approximately north and south lines. Oak Harbor, Fremont, Tiffin and Marion all find the Trenton at nearly the same level, viz., 700 feet below tide. From these points southward a slight westerly trend of the contour line can be observed. In all the later stages of growth of those portions of the state that lie east of the line now traced, a prevalent and monotonous southeast dip is observed, the explanation of which must be found in a general elevation of the land to the west, at right angles to the dip, or in other words, in a northeasterly direction.

9. A greater significance is given to the facts obtained in Newberry's survey pertaining to the dip of the strata in southwestern Ohio, by these later explorations. In default of a better horizon, the Medina shale was adopted in 1870 as a base by means of which dip could be determined, and a number of interesting and important facts were brought out, the full meaning of which could not at that time be understood. The facts then obtained can be generalized as follows: (See Vol. I, page 415).

There is no apparent dip in the Cincinnati axis on an east and west line from the Indiana boundary as far as Springfield and Xenia. Beyond that point the rocks descend at a fairly rapid rate.

The only appreciable dip in the Cincinnati axis is to the northward, and the rate in this direction is very small, varying between three and five feet to the mile.

2. THE NORMAL DIP OF THE STRATA.

The easterly or southeasterly dip of the rocks that begins at the margin of the tract now described as the Cincinnati axis, continues through the subsequent history of the state and constitutes the most important physical feature of its geology. All of the Subcarboniferous and Coal Measure strata, in particular, are affected by it. The southerly element of it gradually increases as we pass to northeastern Ohio, and it is probable that the dip becomes due south at some points in this portion of the state. Beyond the limits of Ohio, in Pennsylvania and West Virginia, the corresponding strata descend sharply toward the westward. These facts considered together, mark out the limits of the arm of the sea in which, and around which, the northern extension of the Appalachian coal field was built up, the Cincinnati axis forming its western boundary. These uniform and continuous southeasterly dips can be explained by the steady growth of the land to the westward, after the fashion already described. The dip is at right angles to the constantly advancing border of the sea. It seldom exceeds thirty feet to the mile, or but little more than half of one degree, in the large way, but it is alternately sharpened and reduced, so that for short distances a much greater fall or much less, may be found. The sections illustrative of the structural relations of our different strata bring these points into clear light.

The facts of our present topography seem to point to an original equality of elevation of those portions of the state that were successively brought under this uplifting force. The western outliers of all of the formations are, at the present time at least, at approximately the same elevation above the sea.

3. OTHER ARCHES AND FOLDS.

The statements already made as to the exceeding regularity of the geological structure of Ohio need no qualification, but this regularity of the state, as a whole, is not inconsistent with the existence of a few minor folds and arches distributed, especially through the eastern half of our territory.

Beginning at Columbiana county on our eastern border, a low axis is found entering the state from western Pennsylvania. It crosses the Little Beaver a few miles above its mouth, near Fredericktown. It was first recognized by White, who named it the Fredericktown anticlinal. (Report on Lawrence county and the Ohio line, 2d Penna. Survey.) It is probably this axis that enters the Ohio Valley near East Liverpool, and that makes the conspicuous arch between that place and Wellsville.

Another slight fold is found along the line of the Cleveland and Pittsburgh Railroad. Its elevation is small and its extent has not been traced. The highest point of the arch on this line is near Salisbury. It may be called the Salisbury anticlinal. It was first noted by Newberry. (Geol. of Ohio, Vol. III, page 94.)

Below Steubenville for a few miles there is an arrest of normal dip, which has the effect and is, probably, the result of a low fold. The Wellsburg gas field is located in this region.

In the counties adjoining Columbiana and Jefferson, already referred to, no axes deserving the name have been thus far found. The search for them has not been thorough, it is true, but the two lines of railway that cross Belmont county, for example, have been examined for folds in the strata traversed by them, with negative results. The same thing is true of Harrison, on its southern side. Stevenson describes a small anticlinal passing through Cadiz. (Geol. of Ohio, Vol. III, page 201.) Throughout these districts, aside from the points named, the strata all seem to lie in their regular planes of slight and gradual descent to the east of south.

In order to test carefully these important facts of structure, a line of levels was run for the survey by Prof. C. N. Brown, from Zanesville to Bellaire, along the Baltimore and Ohio Railroad. The levels were connected at all available points with the geological elements that are due in this field. The results of this careful work are shown in the accompanying section. In it the Cambridge arch is the only distinct anticlinal that appears. There is a slight flattening of dip three miles east of Quaker City, and sundry hints of possible uplift or arrest of dip. The section shows, however, in striking terms, the extreme regularity of structure of eastern Ohio. Other examinations confirm this same view.

Further west and north, however, through portions of Stark, Tuscarawas, Guernsey and Muskingum counties, there is quite a broad and extended tract throughout which the normal dip of the strata is suspended or otherwise interfered with.

At least one well marked fold occurs in this field, the summit of which, on the line of the Baltimore and Ohio Railroad, is at or near Cambridge, and it can accordingly be named the Cambridge anticlinal. The belt of country above referred to lies within the margin of the coal field, and by the arrest of normal descent of the strata the coal seams of the Lower Measures are kept within easier reach than they would otherwise show.

The Cambridge anticlinal was first recognized by Stevenson. (Geology of Ohio, Vol. III, page 220.) He also reports a second fold in the same region.

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