500 GEOLOGY OF OHIO. 
~ Guelph horizon. Of course, surface rock is here alluded to, for, beneath 
the Niagara group undoubtedly occur all other Paleozoic series. Hither 
the great glaciers of the north, at a very remote age, have transported 
and deposited all over this rocky floor, in varied depths, vast quantities 
of clay, sand, gravel, and bowlders, on an average of a hundred feet or 
even more. Through the action of water, or the hand of man, where 
there was no other impediment than a few feet of soil, in five different 
localities, smali areas of the native rock have been exposed. Conse- 
quently little or nothing can be known of the topographical features 
of the underlying beds of rock, though the character and constitu- 
ents can be as perfectly known as were the whole open to view. We 
must know, however, that being a limestone of somewhat irregular 
texture, in many places soft and sandy, in others hard and crystalline, 
and subject to the violence of enormous glaciers, that it would certainly 
present a very haggard, cut-up surface were its covering not so complete. 
In those few insignificant areas the beds appear perfectly horizontal and. 
unbroken, save one exception, and that is unusually interesting, as 
indicating the relative situation of Greenville, and the ancient channels 
of Greenville and Mud Creeks. 
In visiting Dr. Gard’s quarries, which are about a mile and a half 
south-west of Greenville, between the fork of Greenville and Mud 
Creeks (but a little nearer the latter), it is first noticeable that the beds 
of rock are considerably folded, dipping toward the south and east; 
aud also the fact, that in quarrying, the rocks suddenly stop in the adja- 
cent Drift, the strata being traceable for a short distance by scattering 
fragments of limestone as torn off and left. In the digging of the public 
cistern on the corner of Fourth Street and Broadway, the Niagara ledge 
of rock was struck at a depth of ninety five feet below the surface. The 
cistern, though a failure, so far as obtaining an abundant supply of wa- 
ter was concerned, inadvertently furnished knowledge that has proved 
useful in other ways. This measurement may also be regarded as the 
minimum, for at no place in the vicinity, in the sinking of wells, has it 
been reached at a lesser depth. 
Gard’s quarries lie about twenty-one feet below Greenville, conse- 
quently seventy-four feet above the rocks underlying the town. The 
same ledge of limestone crops out at Bierley’s, about four and a half miles 
east of Greenville, and fifteen feet higher than the beds last mentioned. 
At Weaver’s Station, about five miles south of Greenville, Mud Creek 
runs over the horizontal Niagara limestone thirty-five feet higher than 
the same. Consequently, all these facts, together with much other con- 
current testimony which might be given, go to show that Greenville is 
