Geology of Cincinnati. 23 



the first one, and is characterized by certain impressions of ani- 

 mal remains, worm tracks, and marks made by running water 

 over exposed surfaces of mud. These are tolerably constant at a 

 horizon which corresponds in a general way in various parts of the 

 group, such as Obanyon Creek in Clermont County, and in ex- 

 posures, near Lebanon, in Warren County. 



All the beds which make up the deposits about the city are 

 by no means equally rich in fossil remains. Sometimes a thick 

 stratum is found which is absolutely barren of life; and again 

 another will be found where remains are extremely abundant. 

 What are known as the Eden shales, amounting to nearly two hun- 

 dred feet in thickness, seem, in places, to be barren of life, al- 

 though in spots fossils are found in abundance. It has been gen- 

 erally agreed that the bedded rocks of this vicinity were laid down 

 in a deep sea. Now Darwin has shown that thick beds of sedi- 

 ment are seldom deposited except over an area of subsidence, and 

 that it is during this ])eriod of sinking that the greatest number of 

 species of animals are preserved. If, therefore, the theory that 

 the epoch of the second shore line was followed by a time during 

 which the land was gradually subsiding, then there should be some 

 record of it preserved in the increased number of species and 

 specimens of fossil remains. The facts known confirm this theory, 

 as will now be shown. 



From two tables of species given by Prof. Orton in Ohio 

 Geology, vol. I., pp. 398—399, it would appear that fossils are 

 much more abundant above the three hundred foot horizon than 

 below it. This horizon in fact seems to be the beginning of the 

 appearance of many forms unknown in the strata below, and the 

 remains are much more abundant in number of specimens also. It 

 is stated that beds are met with in the upper part of the group, 

 sometimes five and six feet thick made up entirely of the valves of 

 brachiopod shells. ''The free valves," says Prof. Orton,* "can 

 be gathered as perfect in form as sea shells on a modern beach, 

 often retaining the visceral and muscular impressions with the 

 greatest distinctness." Still another proof of the subsidence, and 

 that, too, at a slow rate, is the occurrence at about four hundred 

 feet above low water of about one hundred feet of rock which are 

 almost entirely made up of almost microscopic univalve shells. 



These facts show that the period of the second shore line 

 must have been followed by a second epoch of depression, and 



*Ohio Geol. I., p. 3S2. 



