Two north-south sections in north-central Kentucky show the unconformable relationships of the Lexington, Perryville, and Cynthiana divisions of the Trenton. It is proposed to restrict the term Lexington to the pre-Perryville. The Lexington sequence is typically developed in the region around Lexington and Frankfort, but north and south of this area the upper formations are progressively eliminated. In the northernmost area of outcrop the Jessamine forms thè top; in the southernmost, the mid-Benson.
The Perryville is less widely developed and is overlapped by the Cynthiana over much of the region. The Cynthiana section at Lexington, Frankfort, Gratz and vicinity is the upper half, and less of the more complete section developed marginally to the Jessamine Dome. The relationships of the named divisions of this formation are defined and revised.
The bearing of these stratigraphie relationships on the early history of the Cincinnati Arch is outlined.