GENERAL FEATURES OF ILLINOIAN DRIFT SHEET. 277 



residuary clays formed by a dissolution of the surface limestones of that 

 region. Aside from the deposits noted there are occasional beds of coarse 

 gravel and cobble. The bowlders, as above noted, are usually a foot or less 

 in diameter, but they occasionally reach a diameter of 3 or 4 feet. 



In his report on the glacial boundary' Wright notes the occurrence 

 of till in Campbell County, Ky., on the slopes facing the Ohio River. 

 It extends to an elevation of 350 to 400 feet above the river, but no 

 till or granite pebbles were found on the dividing ridge between the 

 Ohio and Licking rivers, whose general altitude is about 400 feet above 

 the river. He describes a stiff clay deposit containing granite pebbles in 

 western Kenton County at points 7 miles south of the Ohio, and also at a 

 railroad cut at Erlanger, the altitude at Erlanger being 475 feet above tlie 

 river. Grranitic bowlders were also noted in pebbly clay. The heaviest 

 deposits of glacial material yet observed on the Kentucky side of the river 

 are the Split Rock conglomerate in the Ohio Valley and a similar deposit 

 a few miles southeast of Split Rock, both of which were discussed above 

 (p. 261). 



On the north side of the Ohio, in the vicinity of Cincinnati, the 

 Illinoian drift, as previously remarked, forms a neai'l)^ continuous sheet both 

 on the uplands and lowlands. So far as observed the only localities in which 

 the drift is patchy or attenuated are along the brow of the Ohio bluffs and 

 on some of the sharp ridges bordering the Great Miami. Here in places 

 there are only scattering pebbles and bowlders. The upland drift, beneath 

 the surface coating of silt, consists almost entirely of ordinary till, thei'e 

 being but little sand or gravel associated with it. The lowland drift is more 

 variable, there being much sand, gravel, and pebbleless clay as well as till. 

 The upland drift ranges from a thin coating up to a deposit about 50 feet 

 in thickness with a general average of about 20 feet. The lowland drift 

 usually exceeds 50 feet, and in the larger valleys a thickness of about 200 

 feet is attained. The till has a brown or yellow color to a depth of 10 or 

 15, and occasionally 20 or 25 feet. Below this depth it has a blue or gray 

 color. 



Where there has been no erosion the bowlders are entirely concealed 

 by the silt, and they are not numerous on the hillsides or in places where 

 erosion has removed the silt covering. The fact that few bowlders and 



' Bull. U. S. Geol. Survey No. 58, 1890, p. 63. 



