390 GEOLORY OF OHIO. , 



The "first bottoms," or boltom 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 frequently, 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. 



" altemata, Say. Gooiobasis depygls 



" hirsuta, Say. Planorbis trivolvjs. 



" monodon, Kackett. Amnicola lapidaiia, Say. 



" tiyroideus. Suooiuea. sp. ? 



" profunda, Say. 



The conditions under which these shells were accumulated 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 

 growths. 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 an'd 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 archaeological remains abound 

 in Southern Ohio. The extensive and elaborate earthworks of the 



