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LICKING COUNTY. sa 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 hiils, 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 strie 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 Driit 
deposits. In Licking county «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 wanting, and the present sur- 
face has been wholly modified by post-glacial agencies, it may be difficult, 
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 
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 
