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 turr 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. 40 
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. fibratum. Perrysville formation. 30 
5... Granular limestone above, with seven to ten feet of fine- 
grained argillaceous limestone below. Columnaria 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 limestone with Stromatocerium. Benson for- 
mation. 35 
3. Argillaceous limestone with interbedded thin clayey 
layers. Prasopora simulatrix, Rhynchotrema increbes- 
cens, and Hebertella frankfortensis appear first at this 
