398 GEOLOGY OF OHIO. 



and studied to the best advantage, as also in the vicinity of Post Town, 

 on the Banker and Lucas farms. 



To follow their history we must go back to the "Champlain Epoch "of 

 geoloo'y — to the period of submergence that followed the glacial epoch. 

 The level of this portion of the country was at that time four hundred 

 feet lower than at present. Stratified deposits, on a larte scale, of sand, 

 gravel, and clay are found four hundred feet above the present drainage 

 of the country. At th6 period of greatest submergence there could have 

 been little or no current through the valley, but during the slow-advanc- 

 ing movement of depression the valley was filled with immense accumu- 

 lations of re-arranged Drift. We may suppose, then, that the gravel 

 terraces are a part of the old fi(jor of the valley, and ' that they once ex- 

 tended with a degree of uniformity throughout the wide basins in which 

 we find the remnants of them to-day. As the continent emerged once 

 more and slowly regained its present elevation, the river channels would 

 be cut deeper and deeper into these deposits, the former surfaces of which 

 were left one hundred feet or more above the present river beds. 



Little needs to be said in regard to their composition, as the name by 

 which these deposits are known, viz., the gravel terrcuxs, indicates the 

 main element in their making up. Gravel, eand, and loam, variously 

 intermingled, constitute the whole series. The sorting and arranging 

 of materials could only have been accomplished in long-extended periods 

 of time. There are no indications of tumultuous deposition in any por- 

 tion of the series. The soils formed from the weathering and decompo- 

 sition of the surfaces of these beds are kind and productive. 



(&.) The second bottoms, like the terraces, must be referred to causes 

 and conditions not now existing in the valley. They lie above the 

 reach of the highest floods, being thirty feet or more above low-water in 

 the main valley. They occupy broad aieas, and constitute, by way of 

 excellence, the farming lands of the valley. They consist of loams from 

 two to six feet in thickness, overlying gravel which perhaps belongs to 

 section a. They seem to owe their origin to an arrest of the upward 

 movement of the continent, which continued for a considerable period. 



(c.) The first bottoms are the most recent of the series. They are, 

 indeed, very closely connected with the present state of things. They 

 occupy the deeper parts of the valley, and are covered by all of the 

 higher floods. To these floods they owe their origin in part, being made 

 up of the sediments deposited from high water. An arenaceous deposit 

 filled with land-shells is a common and characteristic member of this 

 formation. The shells must have mainly grown upon the regions where 

 we now find them, and were buried by the deposits of annual floods. 



