RAYMOND: CORRELATIOX OF THE ORDOVICIAX STRATA. 259 



horizon, most of them passing up through the Perrys- 

 ville. Three species of Fusispira, and other gastropods 

 are present. Wilmore formation. • 70 



2. Fine-grained Hmestone alternating with clayey layers of 

 similar thickness. Hctcrorthis chjtic, Dalmanella fertilis, 

 Leptacna tenuistriata, and CnjptoUthiis tessellatus are char- 

 acteristic species. Hermitage formation. 22 



1 . Granular limestone with cystids, Edrioaster bigsbi/i, Orthis 



tricenaria, Dinorthis pectinella, etc. Curdsville formation. 23 



On a first survey of the lithological characteristics of the section 

 in central Kentucky, one is impressed by the large amount of light- 

 colored, fine-grained and coarse-grained rather pure limestone and 

 the lack of dark-colored shale. 



Columnaria occurs in the Curdsville, Flanagan, and Cynthiana 

 formations, and Tetradium in the Hermitage, Perrysville, and Cyn- 

 thiana, so that the ^Yilmore and Benson are the only formations 

 without corals. 



Because of the presence of species of Amygdalocystites, Pleuro- 

 cystites, and Edrioaster in the Curdsville in Kentucky it has become 

 the custom to correlate this zone with the cystid zone of Ontario. 

 Ulrich, and following him, Bassler, have correlated the Prosser of 

 Minnesotia with the Curdsville of Kentucky, a correlation not borne 

 out, I think, by the evidence. 



The Curdsville fauna of Kentucky is a pure derivative of the Black 

 River, only the echinoderm fauna being added to a rather typical 

 Leray-Black River assemblage of fossils. 



In Minnesota the Pleurocystites occur in a very diflferent associa- 

 tion. They are found in the lower part of the Fusispira beds (zone 7 

 of the section above) where they are associated with Strophomena 

 trilobata, Cyclospira bisiilcata, and Rafinesquina deltoidea, all Lpper 

 Trenton species in New York and species which are never found so 

 low as the Black River. This zone is also above the Clitambonites 

 bed, which can not be correlated with anything older than the \Yilmore 

 of Kentucky. 



In Ontario there are three "Curdsville" zones, two above and one 

 below the bed which is correlated with the Clitambonites bed of 

 Minnesota. All are seen in the section at Ottawa, where the zones 

 are separated by seventy-five feet of strata containing two distinct 

 faunules. 



The lower zone, to which I have given the formation name Hull, is 



