398 GEOLOGY OF OHIO. 
and studied to the best advantage, as sil f in the vicinity of Post Town, 
on the Banker and Lucas farms. 
Teo follow their history we must go back to the Onan Epoch” of 
geolozy——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 larce scale, of sand, 
gravel, and clay are found four hundred feet above the present drainage 
of the country. At the 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 floor 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 terraces, indicates the 
main element in their making up. Gravel, sand, 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. 
(b.) 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 areas, 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. 
