STRUCTURE OF ILLINOIAN DRIFT BORDER. 269 



About 1 J miles east of Clearport, near the forks of the road, there is a 

 good exposure of buried soil apparently of Sangamon age between the sur- 

 face silt and the lllinoian drift. The soil is a rich black, but the glacial depos- 

 its below are of a pale-ash color and quite sandy. A half mile northeast from 

 the exposure, on a tributary of Clear Creek, is a knoll of lllinoian drift about 

 30 feet high, which at the surface carries a slightly pebbly clay but seems 

 to have a nucleus of gravel. The drift is very scanty from the valley in 

 which this knoll stands eastward to the Hocking Valley at Sugar Grove. 



A black, mucky soil was found between the Wisconsin and lllinoian 

 drift in the grading of the railway leading from ^Lancaster to the reform 

 school aboiit 4 miles south of Lancaster. 



In the Hocking Valley about midway between Sugar Grrove and Lan- 

 caster a few drift knolls appear, one of which, near Crawfiss Institute, has 

 been opened for gravel. The pebbles are largely of limestone and sand- 

 stone, as may be seen by the table below. In making the classification 

 pebbles 1 to 2 inches in diameter were taken. 



Olassificatimi of pebbles in a gra/vel Icnoll in the Hocking Yalley ieloio Lancaster-, Ohio. 



Per cent. 



Granite - 2 



Other pre-Cambrian crystalline rocks ^ 9 



Chert - '- 2 



Quartz 3 



Clay ironstone 2 



Sandstone, probably local - -'- 36 



Limestone "iB 



Total - 100 



The drift in the Hocking Valley has a depth of about 200 feet at Lan- 

 caster and a still greater depth toward the head of the stream, while down 

 the valley the thickness shows a marked decrease. The well data (as shown 

 on p. 169) indicate that the rock floor slopes toward the Scioto Basin, or in 

 the reverse of the present drainage. So far as could be learned from well 

 drillers, the drift in this valley consists chiefly of sand and gravel, there 

 being little, if any, till reported. Occasionally a "blue mud" is mentioned, 

 but it seems to be free from bowlders or coarse rock fragments. The court- 

 house hill in Lancaster has a large amount of cemented gravel in its base, 

 but there is about 40 feet of drift covering the highest part of the hill. The 

 surface drift is till, apparently of Wisconsin age, but the underlying 

 cemented gravel is probably ■ lllinoian. This cemented gravel is well 



