390 GEOLOGY OF OHIO. 
The“ first bottoms,” or bottom lands proper, consist of the flood plains of 
the present rivers. They are composed of gravel—coarse below, large 
slabs of blue limestones being sometimes laid against one another, in al- 
most regular courses, and finer materials upward, the surface consisting of 
clays, loams, or, very fréquently, of a loess-like deposit, of which land 
and fresh-water shells make a notable element. 
The following shells are among those that are found here, all of them 
inhabiting the valley to-day, though in very different proportions from 
those that are shown in these deposits : 
Helix elevata, Say. Helix solitaria. 
“*  concava, Say. <¢ tridentata. 
‘‘  alternata, Say. Goniobasis depygis 
«hirsuta, Say. Planorbis trivolvis. — 
‘¢ monodon, Rackett. Amnicola lapidaria, Say. 
‘¢  thyroideus. Succinea. sp. ? 
‘¢  profunda, Say. 
The conditions under which these shells were accumuiated were prob- 
ably not very different from those that now prevail. The bottom 
lands of previous years were their places of growth and habitation. 
The occasional floods that cover these lands, buried under sandy sedi- 
ments the thickly strewn shells. In some instances, not less than six 
feet of the higher deposits are largely composed of these shells. Since 
the clearing and occupation of the river valleys, these shells are far less 
numerous than before, and, consequently, the sediments of the later 
overflows are not mingled with shells, but are blackened by organic 
erowths. The whole composes a soil of unusual fertility. At some 
points in the valleys, as at Middletown, the whole of the upper series of 
deposits is burned into a cream-colored brick, which, when subjected to 
a high degree of heat, makes a pavement as enduring as limestone. 
The gravel terraces differ from the above-named deposits, in this impor- 
tant particular: their form and structure are not to be explained by the 
conditions that now prevail in the valleys. The materials that compose 
them were associated and deposited in water, but they are situated from 
twenty-five to fifty feet above the highest overflows of the present. 
They point unmistakably to the period of submergence that closed the 
Glacial Period of later geological history. As has been already stated, 
the more detailed description of these beds will be reserved until the 
geology of Butler county—the last of these four blue limestone coun- 
ties—is treated. : 
It is well known that very interesting archeological remains abound 
in Southern Ohio. The extensive and elaborate earthworks of the 
