252 OHIO BIOLOGICAL SURVEY 



the generalized table given. The rocks are all derived from shallow 

 water deposits and like most other such strata vary greatly in thickness 

 and lithogical character within short distances. No single section cor- 

 responding to the table could therefore be found, but the data given 

 are sufficiently accurate for the purposes of tliis paper. 



GEOLOGICAL FORMATIONS 

 Pottfiville. 



10' Blue arenaceous shale. 



3"-18" Coal (Probably the Quakertown Coal, No. 2). Formerly worked at 

 the head of Laurel Run for local consumption. 

 85' / 20' Argillaceous shales and sandstones \\ith some fire clay. 



30' Massive coarse-grained sandstone (the Sharon), but cemented so 



loosely as seldom to form surface rock. 

 20-.S0' Thin-bedded sandstpnes ^vith some impure fire clay and coal blossom. 



Logan formation. 



45' Thin-bedded sandstones with argillaceous or arenaceous shale partings, 



some strata of impure nodular limestone. 



BlacTc Sand Conglomerate. (Upper portion of Ciiyahoga formation), 



200' A single conglomeritic sandstone or several, usually two, heavy sand- 



stones separated Iry intervals of argillaceous shale. 



Cuyahoga formation (proper) 



500' Sandstones, mostly thin-bedded, and shales. The top of the formation 



is exposed in a few places in our area. 



Except for the Black Hand the rocks are seldom exposed except in 

 the bottoms of the ravines and in artificial excavations such as road- 

 side ditches. Their physiographic features therefore recpiire no spe- 

 cial mention, but the peculiarities of the weathering of the Black Hand 

 have a large effect on the physiography and the vegetation of the 

 country. When first (juarried this stone is very friable, but on ex- 

 posure it becomes hard and durable. Thus it often happens that the ex- 

 posed top of a cliff becomes much harder than the protected portion 

 which weathers away more rapidly, forming an overhang. The 

 "caves," as they are popularly called, so formed are very numerous 

 and some of them are very extensive, when the method of their forma 

 tion is considered. The most interesting are favorite places for picnics 

 and a few of them have ac(|uired more than a local reputation. Ash 

 Cave is the largest, being nearly 700 feet long with an overhang 

 of about 60 feet and a height at Ihe waterfall of 84 feet. Old Man's 



