KTCHMOND FAUNAL ZONES IN WARREN AND CLINTON 



COUNTIES, OHIO 



By George M. Austin 

 Of Wilmington, Ohio 



Previous to 1897, when Winchell and Ulrich first used the term 

 " Richmond Group " to designate the uppermost formation of the 

 Cincinnatian series as then considered, no careful or extended work 

 had been undertaken for the purpose of determining the vertical 

 range and variation of its fossils, or to establish the boundaries or 

 lithological characters of its subdivisions. Before that date writers, 

 in describing new species from these strata, made no attempt to 

 designate their exact position in the series, although, as is the case 

 with some of these species, their vertical range does not exceed a 

 very few fe^t. In almost all of these early descriptions of Rich- 

 mond fossils the general statement that the particular species under 

 discussion was from the upper part of the Hudson River group was 

 considered sufficientlj'^ explicit. 



As a result of later investigations during the last thirty years by 

 such careful observers as Ulrich, Nickles, Foerste, Bassler, Cumings„ 

 and Shideler, the boundaries of the various subdivisions of the Rich- 

 mond have been established and the vertical range of many of its 

 species accurately determined. Also in the case of many of the 

 species which first made their appearance in this region during the 

 deposition of the Richmond rocks, much progress has been made 

 in determining their previous habitat and the lines along which 

 they extended their range into this territory. The writer has spent 

 half a century in such studies and with the recent gift of his collec- 

 tion of Early Silurian fossils to the United States National Museum, 

 it was thought fitting that some of his observations be put on record. 



In the present paper it is our purpose first to call attention to a 

 factor which we believe exerted a more potent influence in bringing 

 about the many and often abrupt lithological and faunal changes 

 met with in the Richmond than any other cause of which we now 

 have knowledge. This factor was the oscillation of the sea floor 



No. 2671.— Proceedings U. S. National Museum. Vol. 70, Art. 22 

 l:7«ne— 27 1 



