6 PROCEEDINGS OF THE NATIONAL MUSEUM vol.70 



destroying it, but also deposited more or less heavy beds of nodular 

 clay stone or more frequently one or more compact clay stone layers^ 

 thicker and quite different in character from those common to the 

 group and second, by the breaking down of previous barriers, thus 

 opening the way for the entrance of the many new species which ap- 

 pear abruptly in the Richmond strata just above or more rarely 

 below these peculiar argillaceous deposits. Thus we are convinced 

 that the changes produced in our Richmond seas by these outside 

 disturbances were largely responsible for those differences which 

 have made it necessary, or at least convenient to divide the group 

 into its present recognized divisions and that those peculiar clay 

 stone layers truly indicate the natural lines of demarkation between 

 them. With one exception, the point of contact between the Fort 

 Ancient and Clarksville, the lines of junction between all the divi- 

 sions are clearly marked in this region by the presence of these 

 unusual argillaceous deposits. 



In conclusion we would say that the following lists lack much of 

 being complete. There is quite a number of species in the group 

 which have not been named and described, others present are so rare 

 in their occurrence that we have failed to find them in this territory, 

 while many more in such classes as the bryozoans and gastropods 

 we have not been able to identify. 



Again, in attempting to find out the vertical range of the various 

 species of a division or of a group, one is certain to meet with the 

 greatest difficulties if they are attempting a reasonable approach to 

 accuracy. In numerous cases an individual may be unexpectedly 

 found much below or far above where the species attains its full 

 development in numbers. Other species, though present in the 

 group are so rare that one is lucky to find a single specimen during a 

 lifetime search. Still other species were restricted in life to widely 

 scattered colonies, the remains of which may not through long 

 periods be uncovered at any of the exposures in the territory. 



Our classification of the Richmond strata in this area is given in 

 the following composite section : 



COMPOSITE SECTION OF THE RICHMOND GRODP IN WAKRiaN AND CLINTON COUNTIES. OHIO 



Elkharn formation (Beds E. 1-3) 



Upper division (E. 3). Blue clay, unfossiliferous except that a few layers 

 15 feet above the base contain Cyphotrypa stidhami and Ctcnodonta hilli 

 in abundance and the top stratum holds the species of annelids described 

 by Foerste 42' 



Middle division (B. 2). Thin bedded blue limestone with a few clay layers 

 containing Homotrypa worthcni prominens, Platpstrophia moritura, Opis- 

 thoptera casei, and Lichenocrinus ttibercukitus with ^treptelasma rusticum^ 

 Protarea richtnondensu, and other longer ranging fossils 4' 



Lower division (E. 1). Fossiliferous blue clay with Ischyrodonta elongata^ 

 I. misetwri, Bellerophon mohri, etc 2' 



