192 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



the correlation of the beds lying between the horizon of the " Black 

 shale" and the base of the Burlington limestone as carboniferous. 

 Their argument was as follows : On passing westward from New 

 York, the representative of the Chemung in Ohio offers considerable 

 change in the paleontologic characters, and between the correlated 

 faunas of Ohio and Michigan, a still greater difference is seen. Yet 

 we feel warranted in regarding them " as of the age of the Chemung 

 group of New York, and, so far as we know, no one has questioned it. 1 " 

 They were l< confident that some of the species found at Burlington 

 and other places in the west of the same geological horizon are iden- 

 tical with some of those found in the Chemung rocks of Ohio, which 

 rocks can be traced continuously to New York," and, " notwithstand- 

 ing their carboniferous character, we think their reference to the 

 Chemung of New York legitimate and proper. 2 " They accounted for 

 M. de Verneuil's correlation of the " Chemung " of Ohio as carboniferous 

 by supposing that he was ignorant of the tendency to chauge on pass- 

 ing westward, which they believed belonged to the faunas. They fur- 

 ther maintained that " a direct continuity of the strata of the Chemung 

 Rocks of New York can be traced from that State to those of Ohio," 

 and that Hall considered that but for the Cincinnati axis the con- 

 tinuity could be traced to the Mississippi Valley. They noticed the 

 difference in faunas, but believed with Hall that a stratigraphic con- 

 tinuity had been established. 



When we examine the argument critically, we find that the error was 

 at the start, on passing from Chautauqua County, New York, to Ohio. 

 It was supposed that continuity of strata had been traced, and, in spite 

 of the difference observed between the species in the Ohio rocks and 

 those of the New York Chemung, the belief in the identity of strata led 

 to a theory to account for the difference of fossils. 



This is one of the best illustrations we have seen of the principle that 

 correlations by lithologic characters cannot be relied on, even when the 

 continuity is affirmed by a careful geologist after a special survey. 

 Whereas the testimony of fossils can always be relied on to the extent 

 and with the precision which our ability to interpret them will permit, 

 and the reason is not far to seek. Petrographic characters have no re- 

 lation to age. The characters of fossils are intimately associated with 

 the time and environment of the living organisms they represent. 



1 " Observations on the rocks of the Mississippi Valley which have been referred to the Chemnng 

 group of New York, together with descriptions of new species from the same horizon at Burlington, 

 Iowa," by C. A. White and It. P. Whitfield. Boston. Soc. Nat. Hist., Proc, vol. 8, pp. 289-306. Re- 

 viewed by "Anon." Am, Jour. Sci., 2d ser., vol. 33, p. 200. 



