KENTUCKY SECTION 573 



The Benson is a thinly bedded limestone;, about 35 feet thick., with 

 Dinorthis ulriclii, Strophomena vicina, and a layer of Stromatocerium in 

 its upper portion. It is not separated very sharply, either faunally or 

 lithologically, from the Jessamine below. 



The latter formation, about TO feet thick, consists of thinly bedded 

 limestone with rather thick shaly partings, and is the zone of Prasopora 

 simulatrix. It also contains many of the common Trenton fossils, such 

 as Zygospira, Pleetambonites, and Dalmanella. It shares with the other 

 subdivisions of the Lexington the brachiopods Hebertella frankfortensis 

 and Rhynchotrema increbescens and seemingly lacks any representative 

 of the genus Platystrophia. 



Beneath is the Logana, 25 to 35 feet in thickness, made up of somewhat 

 clayey limestone and shale, the characteristic fossil being the exceedingly 

 rare Heterorthis clytie. What is more significant, this formation oc- 

 casionally furnishes Cryptolithiis tessellatus, which I was fortunate 

 enough to find at this horizon in the section at the Old Crow distillery, 

 on Glenns Creek, and which Foerste has previously listed, although with- 

 out locality. 3 



The lowest bed of the Trenton succession, the Curdsville, is rather 

 sharply set off from the Logana above as a massive, coarsely granular, 

 gray limestone about 10 to 12 feet in thickness. It in turn rests upon 

 the Tyrone with a "welded" contact. The upper layers of the older 

 formation show shrinkage cracks, indicating emergence after their de- 

 position. 



Correlation 



Aside from its exotic series of Echinoderms, which have no great value 

 in correlation, the fossils of the Curdsville ally it closely to the Leray of 

 Xew York, with which it has sometimes been correlated. Such species 

 are Keceptaculites occidentalis, Streptelasma profundum, Columnaria 

 halli, Orthis tricenaria, and a large fauna of mollusca. This summer, 

 however, I found a number of specimens of a Platystrophia which is 

 probably the form called P. trentonensis by McEwan. This indicates a 

 somewhat mixed Trenton and Leray fauna, such as is found in the Rock- 

 land in Ontario. 4 



The presence of Cryptolithus tessellatus, Dalmanella, and Mesotrypa 

 quebecensis in the Logana, together with its relation to the Jessamine 

 above, is sufficient to correlate the formation in a oeneral way with the 



a Kentucky Geol. Survey, ser. 4, vol. 1, pt. 1, 1913, p. 372. 

 4 A. E. Wilson : Dept. Mines Canada, Bull. 33, 1921, p. 19 et seq. 

 P. E. Raymond : Geol. Survey Canada, Sum. Rept., 1912, p. 399. 



