598 GEOLOGY OF OHIO. 



well marked portions. From the north line of the county, almost to the 

 city limits of Columbus, the river has worked out its channel in heavy 

 beds of Devonian limestone. In the vicinity of Dublin, the vertical 

 wall is between forty and fifty feet in height, and the real depth of the 

 excavated valley is not less than 125 feet. The most picturesque scenery 

 of the county, is shown in the gorges of the Scioto and its larger tribu- 

 taries in this region. But, through all this pait of its extent, the valley 

 is very narrow, the bottom lands being of comparatively small extent, 

 and often being entirely wanting. As the river approaches Columbus, 

 its eastward course carries it beyond the outcrop of the limestones into 

 the softer beds of the Huron shale, and from this point on, the character 

 of the valley is very different. It is no longer confined to the river 

 channel, nor even to the broad bottom lands that border it, but widely 

 eroded regions, now filled with heavy and irregular deposits of Drift, at- 

 test the former presence of the river at paints several miles removed 

 from its present limits. In Hamilton and Jackson townships, especially, 

 the boundaries of the valley are quite indistinct, the second bottoms 

 often merging imperceptibly into uplands somewhat more elevated, but 

 not separated from them by any obvious line of demarkation. For sev- 

 eral miles, on either side, the altitude is but little greater than that of 

 the valley proper. In Hamilton township, indeed, and also in Madison, 

 very extensive erosion of the bedded rocks must have taken place. 



The valley of the Whetstone, or Olentangy River, also constitutes a 

 very prominent feature of the northern half of the county. It enters the 

 county west of the middle point of its northern boundary, and flows 

 almost due south, until it enters the Scioto at Columbus. Throughout 

 all of this district, it has been excavated in the easily eroded shales of 

 the Huron system. It furnishes, by comparison with the Scioto Valley, 

 at points due west of it, a striking example of the disparity with which 

 difierent geological formations resist wear and waste. The levels run in 

 the construction of the Worthington and Dublin turnpike, show that 

 low water in the Olentangy, west of Worthington, is sixteen feet lower 

 than low water in the Scioto at Dublin. The Scioto exceeds the Olen- 

 tangy several times in volume, and, other things being equal, its valley 

 should be much deeper. It is also to be noted that the disparity would 

 be still more striking, if the actual depths of the valleys were taken 

 into the account. The Olentangy runs upon Drift beds, the shales 

 having been cut out to an unknown, but probably considerable depth, 

 while the Scioto, at the points named, has a rocky floor. The contrast 

 between the valleys, in width, is equally marked. As already stated, 

 the Scioto Valley, in the northern half of the county, is but a narrow 



