Silurian Fossils. 5 



county, is found immediately above the sandy layers contain- 

 ing WhitHeldella suhquadrata, Foerste. The ore is overlaid 

 at the Rose Run quarry by eight feet of Plum creek clay and 

 five feet of Oldham limestone. The sandy layers containing 

 WhitfieldeUa suhquadrata appear to locate a stratigraphic 

 break, distinctly sandy layers being rare in Silurian rocks in 

 Kentucky or Ohio, and on this account the sandy rock with 

 the overlying* iron ore has been included w^ith the overlying 

 Crab Orchard formation, rather than with the underlying 

 Brassfield bed. 



It will be a subject of future inquiry to determine whether 

 the Alger clay division of the Crab Orchard formation of 

 Kentucky corresponds to all or only to the upper part of the 

 Clinton of Maryland, as identified by Prouty. 



The most interesting result, however, of this attempted 

 correlation of the Silurian formations of Kentucky with those 

 of Maryland is the conclusion that the low barrier separating 

 the Cumberland gulf, containing the Maryland and eastern 

 New York Silurian deposits, from the interior epicontinental 

 sea, containing the Kentucky and Ohio Silurian deposits, was 

 lowered several times during Silurian times. It must have 

 been lowered during the deposition of the upper parts of the 

 Alger clay, so as to permit of the entrance of Calymcne clin- 

 toiii into Kentucky. It probably was lowered again during 

 the deposition of the lower part of the West Union bed, 

 although Daluumitcs liuiulurus and HonwlaJiotus dclphino- 

 ccphalus occur abundantly in the Rochester shale of western 

 New York. Some of the associated species, at Martins, in 

 Kentucky, however, remind me more of Cumberland Gap and 

 Alabama fossils than of those of western New York. 



Again, during the deposition of the Waco limestones, an 

 Atlantic fauna including Calostylis appears to have come in 

 from some point eastward. ' 



It should be stated, however, that this incursion of eastern 

 faunas appears to have been local. The Waco fauna is con- 

 fined practically to Madison, Estill, Powell and Clark counties. 



