PROFESSOR SAFFORD's OBSERVATIONS 421 



Clinton of eastern Tennessee. This will make clear also the following 

 quotations : * 



"Upon entering the Central basin from the east, the featheredge of the Meniscus 

 limestone is met with on the northern side, in Macon county, and on the southern, 

 in Lincoln, and in the southwestern part of Bedford. 



"The (Meniscus) series is divided into two nearly equal members, the sponge- 

 bearing bed above and the variegated bed below. 



" It is the upper member of the Meniscus formation, for the most part, that ap- 

 pears on the slopes of the Central basin ; the variegated bed presents itself mainly 

 in the Western valley and in its ramifications." 



The sponge referred to is the Astrseospongia meniscus. 



It is evident that Professor Safford was of the opinion that the Cin- 

 cinnati anticline was in existence already in Silurian times, since he 

 states that the Niagara and Lower Helderberg are unconformable to the 

 Nashville beds, although he nowhere offers any reason for believing in 

 this unconformity. The problem of a possible unconformity between the 

 Ordovician and Silurian still remains to be solved by some investigator. 



Professor Saflford appears also to be of the opinion that the upper beds, 

 consisting of the Meniscus or sponge-bearing beds, overlapped the lower 

 or variegated beds, and hence were more commonly exposed on the 

 western slopes of the Central basin. He probably held the idea that 

 the anticline was sinking during Silurian times, and that on this account 

 the upper beds progressively overlapped the lower ones. It may be 

 seen, however, from the accompanying map and sections, that the equiva- 

 lent of the sponge-bearing bed, the Louisville limestone, is by no means 

 as frequently exposed, nor does it extend as far eastward up the anti- 

 cline in its present condition as the equivalents of the variegated beds — 

 the Laurel, Osgood, and Clinton beds of this paper. 



In the Elements of the Geology of Tennessee, by Professor Safford and 

 Doctor Killebrew, the name " Clifton limestone " was adopted for that of 

 the Meniscus limestone. Even at the type locality this limestone in- 

 cludes all of the horizons from the Clinton to the Louisville, except the 

 Waldron shale, which has not been identified in the western valley of 

 the Tennessee river. 



SILURIAN EXPOSURES ON THE UPPER CUMBERLAND, SOUTHERN KENTUCKY 



The eastern border of the area along the crest of the Cincinnati anti- 

 cline within which no Silurian rocks are preserved can not be determined 

 with certainty in Tennessee, since no outcrops occur in those regions 

 where this border must be sought. It may be located, however, east of 



* Page 313. 



