THE DATE OF TEE GLACIAL PERIOD. 561 



ago, this stream, a few miles above its junction with the 

 Scioto, at Chillicothe, abandoned its preglacial valley in a 

 most singular manner.* The preglacial valley of Faint 

 Creek for about twenty miles above its junction with the 

 Scioto runs in a northeast direction from the town of Bain- 

 bridge. The valley is nearly a mile wide at the bottom, and 

 about live hundred feet below the general level. But the pres- 

 ent stream, after it has abandoned this old valley, occupies 

 for two or three miles a narrow gorge not over five hundred 

 feet wide, cutting directly through the table-land, and re- 

 entering the old valley considerably lower down in its course. 

 The only satisfactory explanation of this is found in a study 

 of the local glacial phenomena. The lower or northeastern 

 part of this preglacial valley is exactly on the line of the gla- 

 cial boundary, and was for a certain period obstructed by the 

 most advanced portions of the glacier, which dammed up 

 the water and raised it to a level at which it would be forced 

 in front of the ice across a tongue of the table-land, thus 

 eroding the present channel. + 



This portion of the channel, as already indicated, is about 

 three miles long, from three hundred to five hundred 

 feet deep, live hundred feet wide at the top, and two hun- 

 dred at the bottom. The walls near the top consist of fifty 

 or sixty feet of Waverly sandstone, while all below is a soft 

 shale crumbling very readily. The question in glacial chro- 

 nology is to find the age of this gorge, which is clearly post- 

 glacial. The true solution of the problem comes from a 

 study of one of the lateral gorges formed by a small tributary 

 entering the main gorge midway from the south. This 

 tributary, though dry a portion of the year, is at other times 

 a raging torrent, and drains an area of two or three square 

 miles. Yet in the soft shale, so favorable for rapid erosion, 

 it has worn a gorge less than six hundred feet long, but hav- 

 ing a mouth of nearly the same width where it joins the 



* M Geological Survey of Ohio," vol. ii, p. 653. 

 \ See map, p. 373. 



