782 GEOLOGY OF OHIO. 
the whole, the soil, from the causes mentioned, is much lighter than that 
of the two counties named, and the sheet of Drift material is thinner 
and less regular in its distribution. 
Glacial marks are seen on the exposed surfaces of the harder rocks in 
nearly all parts of the county, and they are specially noticeable on the 
sandstone ledges on the south-east side of the Mahoning, in Youngstown 
and Poland, and on the higher strata of the same character in the south- 
ern part of Canfield and Elsworth. The direction of the glacial scratches 
is nearly north and south; but they are sometimes deflected by local im- 
pediments a few degrees either east or west. 
One of the most interesting features in the surface geology of Mahoning 
county, is the deep erosion of the valley of the Mahoning. In Trumbull 
county the river flows through a gently undulating country, and its 
banks are so low that it can hardly be said to have a well-defined valley. 
This is due to the general prevalence of soft, shaly rocks which have been 
broadly and evenly eroded. Soon after entering Mahoning county the 
river encounters the Conglomerate and the heavy-bedded sandstones that 
overlie the lowest coal. These form bold bluffs which gradually approach, 
until at Lowell the valley is quite narrow, and about three hundred feet 
deep. It has at one time, however, been still deeper, for the search for 
oil, which has been made at numerous points between Youngstown and 
Newcastle, has shown that in this interval the river is now running 
considerably above its ancient bed. At the State line it was found nec- 
essary to sink through eighty feet of sand and gravel in the old channel 
before solid rock was reached; and in some wells, near the junction of 
the Mahoning and Chenango, pipe was driven one hundred and forty feet 
to the rock. These facts were among the first observed of those which 
led to the discovery that our principal rivers were once flowing at a lower 
level, when the continent was higher than now; a subject which is 
treated at length in the chapter on Surface Geology, which forms the in- 
troduction to Vol. II of this report. The valley of the Mahoning, which 
is evidently excavated from the solid rock, must have been cut out when 
the drainage southward was much freer than at present, and this seems 
to have been one of the channels through which the lake basin, tilled to 
a much higher level than now with water, communicated with the Ohio, 
and thus with the Gulf. The fact that rock is frequently seen in the 
bottom of the river does not conflict with the statements made above, 
for the stream does not follow the line of its ancient bed; but when the 
old channel was filled, and the work of excavation began again, the © 
course of the river often crossed projections from the sides of the valley, 
and in these places has a rock bottom. The borings to which reference 
