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 Ellsworth. 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 graduUlly 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, filled 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 



