LICKING COUNTY. 351 



rocks exposed in the deeper ravines under the influence of surface ero- 

 sion, only form terrace-like slopes, each bench in the hill marking the 

 outcrop of the softer and more easily disintegrated material. Wherever 

 a spring flows out over these argillaceous strata, under the combined in- 

 fluence of the water and the frost, the harder beds above are undermined, 

 are finally broken, and fall by their own weight. This process being 

 continually repeated, the gorge gradually eats its way into the hills, fol- 

 lowing the sinuous .course of the subterranean streams, and resulting in 

 valleys many times greater than could be caused by surface water alone. 

 After the torrents which accompanied the retreat of the ice sheet to the 

 north had expended their force here and further north, removing nearly 

 all the typical glacier Drift deposits, leaving only stratified beds of sand 

 and water- worn pebbles, and exposing in many places the sharp outcrops 

 of the rocks, the subsequent excavating agencies were mainly these 

 springs. The small streams pouring into the valleys over precipices 

 formed by the springs, aid in the work, but are only a supplemental 

 agency. All these causes, together with surface disintegration and ero- 

 sion, combine to produce the conditions described by Prof. Andrews in 

 the south-eastern part of the State. No glacial strise or ice-polished sur- 

 faces are seen, nor are there any crushed outcrops of the rocks, or typical 

 glacial clays, water-washed and stratified material being the only Drift 

 deposits. In Licking county t s in Knox, patches of bowlder clay on the 

 tops of some of the highest hills, and in places below the beds of the 

 lowest streams, still remaining, bear witness to the action of the Drift 

 agencies, the results of which are so conspicuous in the northern counties. 

 Farther south, where these phenomena are waating, and the present sur- 

 face has been wholly modified by post-glacial agencies, it may be difi&cult, 

 perhaps impossible, to determine whether glacial deposits once covered 

 the surface and have since been removed, or whether we have passed 

 southward beyond the original area of the Drift. 



In places in this county unstratified bowlder clay rests upon deposits 

 of stratified sand and gravel. Near the eastern line of Union township 

 an excavation gives the following section : 



1. Unstratified bowlder clay 8 feet. 



2. Stratified sand and gravel to bottom of exposure. 



The rock fragments in this bowlder clay are not striated, but are irregu- 

 lar and angular in shape ; many of limestone and other local rocks ; a 

 small percentage granitic. 



On the banks of the Licking north of Newark old water-plains can be 



