718 GEOLOGY OF OHIO. 



The banks of the Ohio at Steubenville are bold and high, and are 

 composed of horizontal strata which are seen to correspond closely on 

 both sides ; hence we may conclude that they were once continuous, and 

 that the gorge that separates them has been excavated by the river. 

 The reason why it is cut so far below the present stream is that at a cer- 

 tain period the continent was higher above the ocean level than now, the 

 drainage was more free, and the Ohio and other tributaries of the Missis- 

 sippi ran for ages with rapid currents until they had deeply excavated 

 their channels. Subsequently a depression of the continent set back 

 the water in these channels and caused the deposit in them of the ma- 

 terial transported by the smaller tributaries. In this manner the valley 

 of the Ohio was filled to the height of its highest terrace. Afterward 

 the continent rose again, the drainage became freer, the work of excava- 

 tion was resumed, and the present stream has cut so deeply into the 

 material under which its old bed is buried as to leave portions of it 

 standing in terraces of gravel, sand, etc., much above the highest points 

 reached by its floods. Two distinct terraces mark the banks of the pres- 

 ent river in numerous localities ; one the flood-plain, covered in extreme 

 high water ; the other much higher, and marking the level of the old 

 filling of the valley. 



No tests have been made which determine with accuracy the depth of 

 the old channel along the river front of Jefferson county, but from bor- 

 ings made for oil on the Beaver and other tributaries of the Ohio, we 

 learn that they are in some instances cut down one hundred and fifty 

 feet below the present water surface. We may therefore conclude 

 that the bottom of the old channel at Steubenville, is at least one hun- 

 dred and fifty feet below the river, and it may be, considerably 

 lower. No rock was found, as I am informed, on which to place the piers 

 of the railroad bridge, and they are built on cribs. It is also reported 

 that the efiort to drive galleries from the bottom of one of the coal shafts 

 in Steubenville, under the river, was rendered abortive by the flood of 

 water which poured in from above ; this was probably caused by the ap- 

 proach of the gallery to the loose material that fills the old river bed. 



GEOLOGICAL STRUCTURE. 



Jefiferson county lies wholly within the limits of the Allegheny coal 

 field, and all the rocks exposed here belong to the Coal Measures. Of 

 these strata a thickness of nearly one thousand feet are included in the 

 sections obtained by an examination of the hills bordering the Ohio 

 Valley, and by the shafts which have been sunk below the river. A 

 very fair exposition of the geological structure of Jefierson county is 



