MAHONING COUNTY. 783 
hag been made prove that there is a continuous, 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. Asa 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. 
