- GeoRef, Copyright 2008, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
The abundant ledges of limestone characteristic of the type Cincinnatian in the Ohio Valley can be grouped into several classes on the basis of a few criteria that are readily recognized in the hand specimen. Such a classification can make rock descriptions much simpler for those who measure sections there; furthermore, closer correspondence is now possible between the rock descriptions used or published by different workers. The petrographic properties of the 7 classes are fully described and illustrated, although the limestone types are readily distinguished as follows: 1) Fabric of whole and broken fossils randomly arranged; insoluble fraction small and localized. 2) Fabric of broken and whole fossils oriented parallel to bedding; insoluble fraction moderate in amount and localized or disseminated. 3) Fabric of whole and broken fossils, either oriented or randomly arranged; insoluble fraction large. 4) Fabric of finely broken fossil debris; insoluble fraction small and disseminated. 5) Fabric of finely broken fossil debris; insoluble fraction moderate to large; rock laminated or cross-laminated. 6) Fabric of very finely broken fossil debris; insoluble fraction large. 7) Like number 6, but occurs as nodules.