482 E. O. TJLRICH CORRELATION OF THE STRAND-LINE 



wrong when the beds containing the best development of the genus were 

 found to be of Upper Cambrian age. 



The peculiar cephalopod, Gonioceras, long believed to indicate a late 

 Black Eiver age, is now known to range downward almost to the base of 

 the Chazyan series. 



And so it goes with other genera as we pass up the geological column. 

 Several instances, known to me for many years, but only recently pub- 

 lished, are concerned with the much-discussed Devonian or Mississippian 

 age of the Bedford shale of Ohio. Three genera of brachiopods — Pho- 

 lidops, Delthyris, and Nucleospira — cited in paleontological literature 

 prior to 1914 as confined to beds beneath the top of the Devonian, are 

 represented by one or two species each in the Bedford. This fact was 

 mentioned in 1912 by a prominent paleontologist as indicating the Devo- 

 nian age of the formation. Evidently he was not aware that the Missis- 

 sippian contains more species of Delthyris than are known to occur in the 

 Devonian, and that Nucleospira is about as well represented in the 

 younger system as in the older. As for Pholidops, the oldest known 

 species of this persistent genus is found in the lower part of the Ordo- 

 vician; and the survival of the generic type into the Bedford is of no 

 more significance in deciding the age of this formation than attaches to 

 the long-known presence of Leptama, another common Ordovician, Silu- 

 rian, and Devonian genus in the Burlington limestone. 



EXPANSION OF THE VERTICAL RANGE OF GONIOCERAS 



To more clearly illustrate the point that it is desired to make regarding 

 the uncertain value of generic alliances in correlation, the case of Goni- 

 oceras may be given in some detail. 



For more than 50 years Ave have known that Gonioceras is to be found 

 at Murfreesboro, Tennessee. But this Tennessee occurrence — perhaps 

 largely because it is found there with an Iiormoceras that was identified 

 with Hormoceras tenuifilum, the constant associate of Gonioceras anceps 

 in the original New York localities — was accepted as establishing the 

 Black Eiver age of the limestone at Murfreesboro. It was only after the 

 Lowville limestone, which underlies the Gonioceras anceps zone in New 

 York, was recognized in Pennsylvania and thence traced southwardly into 

 Tennessee, where it lies far above the beds containing Gonioceras and 

 Hormoceras at Murfreesboro, that we began to see how widely different 

 in age are the New York and Tennessee occurrences of these cephalopods. 



But this was only the first stage in the revision of prevailing belief 

 regarding the age indication of Gonioceras. Ensuing stratigraphic in- 



