MAHONING COUNTY. 783 



has been made prove that there is a coatinuous, deeply-excavated trough 

 running beneath the bottom lands of the valley. 



GEOLOGICAL STRUCTURE. 



The rocks which underlie Mahoning county all belong to the Carbo- 

 niferous System. They include exposures of the Waverly at base, the 

 Conglomerate, and all the lower group of coal seams, except the upper- 

 most. No. 7, with their associated sandstones, shales, limestones, fire- 

 clays, and iron ore. The dip of all the strata is toward the south-east, 

 from ten to twenty feet to the mile ; and, as a consequence, the outcrops 

 of the different members of the series form irregular belts conforming to 

 the topography, but having a general east and west direction, the out- 

 crops of the rocks, which are lowest geographically, being lowest topo 

 graphically, and found on the northern margin of the county, while the 

 highest cap the hills along the southern boundary. 



WAVERLY GROUP. 



This consist of a series of shales and sandstones of which the entire 

 thickness is from four to five hundred feet. In the counties futher north 

 where better exposed, this formation is seen to be composed of a num- 

 ber of sub-divisions which have received distinct names, viz., the Cuya- 

 hoga shale, the Berea grit, the Bedford shale, and the Cleveland shale ; 

 the latter resting upon the Erie shale, which form the lake shore and 

 underlie the surface throughout a large part of Ashtabula county. The 

 only portion of the Waverly Group exposed in Mahoning county is the 

 Cuyahoga shale, which is excavated to form the bed of the Mahoning 

 River from Niles to the State Line. Not more than fifty or sixty feet of 

 the formation is any where shown. This consists of yellow or olive argil- 

 laceous shales with beds of laminated sandstone. It contains few fossils 

 here, and is rarely hard enough to serve as a building stone. As a con- 

 sequence it has no interest or value, except as it forms the " bottom 

 rock " reached in many of the borings for coal, and therefore serves an 

 important purpose in limiting the search, as it is well known that no coal 

 can be found below or in it. 



The extensive explorations for coal made in Mahoning county show 

 that the Waverly rocks for a long time formed the surface, and were ex- 

 tensively eroded before the deposition of the next succeeding rock, the 

 Conglomerate. Hence its upper surface is very irregular, showing hills 

 • and valleys over which the Conglomerate and Coal Measures were 

 deposited; sometimes in local depressions with Waverly borders, so that 

 both are found at a lower level than adjacent outcrops of Waverly rock. 



