The Ciuciniiatiaii Series and its Brae liiopods. 37 



A number of liiiicstone sinks are known in the Cincinnati 

 quadrangle in places immediately underlain by the Bellevue, 

 which contains some of the purest limestone strata of the 

 series. They probably owe their existence to the falling in 

 of the roofs of caverns which were formed by the solution 

 of the Bellevue limestone. 



III. Geologic and Physiographic History 



A. Paleozoic Era 



1. Cincinnatian epoch. — During the Cincinnatian epoch 

 the interior of the continent was a vast epicontinental sea, 

 with land to the east, north, and west. Toward the close 

 of the Mohawkian epoch the sea became shallow enough to 

 affect the character of the sediments. The Winchester and 

 Lexington limestones (Mohawkian) of central Kentucky 

 and the Bromley and Pt. Pleasant (Trenton) of northern 

 Kentucky and southwestern Ohio, which contain upward 

 an increasing amount of shale, give evidences of the shallow- 

 ing of the epicontinental sea in the Cincinnati region. The 

 wave-marked limestone layers composed of fragmental 

 material and the mud-balls of the Pt. Pleasant indicate that 

 the sea had become quite shallow. A slight disconformity 

 exists at the top of the Pt. Pleasant, pointing to a short 

 emergence of this area at that time. 



Eden stage. — Throughout the Eden stage the sea re- 

 mained quite shallow and a large part of the material 

 deposited was mud. The mud-balls and wave-marked 

 limestone layers of this formation previously described also 

 indicate shallow water deposition. The amotmt of material 

 deposited (230 feet) was far greater than that of the two 

 subsequent stages, and almost equal to that of the Rich- 

 mond. The life of the Eden stage was meager for the muddy 

 waters were unfavorable to abundant life. Bryozoans, 

 though not abundant, were fairly well represented, and 

 trilobites (Calymene and Isotelus) and pelecypods (Bysson- 

 chia) were not uncommon. 



