258 bulletin: museum of comparative zoology. 



higher beds of the Trenton series and how, as time went on, their own 

 faunal content became changed, showing that it was not a sudden 

 migration of the sea over a tilted and partially eroded series of earlier 

 deposits, but that the near shore black shales were able constantly to 

 encroach upon the portion of the sea where limestone was forming 

 till it finally progressed over the entire northern and eastern portion 

 of the sea. 



If we now turn to the south, we find that in Kentucky and Tennessee, 

 clear water conditions prevailed throughout the Trenton and conse- 

 quently there were very different faunas, a fact best expressed in the 

 presence there throughout the Trenton of the corals Columnaria and 

 Tetradium. 



Kentucky. 



The following is a section in central Kentucky, after Foerste (102). 



7. Granular limestone above, argillaceous limestone and Feet. 

 clay below. This formation is referred to the Eden by 

 the Kentucky geologists. Along the Ohio River oppo- 

 site Cincinnati it contains Cryptolithus in abundance 

 and in northern central Kentucky it contains a fauna 

 very closely allied to that of the Eden and Maysville. 

 Cynthiana formation. -iO 



6. Granular limestone in the upper five feet, nine feet of 

 dense white limestone below, and twenty to twenty-five 

 feet of fine-grained grayish limestone at the base. The 

 fauna is large, containing many gastropods and pelecy- 

 pods, several brachiopods, and two species of Tetradium, 

 T. columnare and T. fihratum. Perrysville formation. 35 



5. Granular limestone above, with seven to ten feet of fine- 

 grained argillaceous limestone below. Columyiaria alveo- 

 lata is present in the upper part, and the lower bed is the 

 one from which the Brachiospongia have been obtained. 

 It contains the oldest Platystrophia and Clitambonites 

 found in the Kentucky section. Flanagan formation. 60-70 



4. Granular hmestone with Stromatocerium. Benson for- 

 mation. 35 



3. Argillaceous limestone with interbedded thin clayey 

 layers. Prasopora simulatrix, Rhynchotrcma increbes- 

 cens, and Hebertella jrankfortcnsis appear first at this 



