GIRTY, GEOLOGIC AGE OF THE BEDFORD SHALE 297 



the top of the Bedford is offset by one equally marked in the opposite 

 direction, between the Bedford shale and the Chagrin shale. In support 

 of this statement I shall not feel called upon to submit evidence, because 

 in so far as it is untrue, the Devonian affinities of the Bedford faunas are 

 by so much stronger than they are here represented. Finally, the deter- 

 mination of the boundary between the Devonian and Carboniferous at 

 the base of the Berea satisfies to some extent the canon of convention. 

 This is true, however, only from one point of view, for if the Berea 

 ("Cony") sandstone correlates with the Kinderhook beds of the Missis- 

 sippi Valley which represent the base of the Carboniferous system in its 

 type section, and if some horizon below (?) the Chagrin correlates with 

 the Chemung group which represents the top of the Devonian in its type 

 section, 3 the canon of convention or usage would be ambiguous in its 

 bearing upon these intermediate beds whether they should be classed with 

 one system or the other, because by one approach they would be found 

 above the recognized top of the Devonian, just as by the other they would 

 be found below the recognized base of the Carboniferous. 



This too is only partly true, however, because Hall 4 classed as Che- 

 mung, or more often "Upper Chemung," the intermediate group of 

 strata here under consideration, so that, although their stratigraphic 

 position is above the Chemung proper and therefore theoretically above 

 the top of the Devonian, they have in practice been included all along in 

 that system. Incidentally, this circumstance seems to show Hall's opin- 

 ion of the affinities of the "Bradfordian" faunas, 5 though it must be re- 

 membered that he correlated with the Chemung the Waverly group lying 

 still above. 



Now the statements which it is proposed to present the evidence for 

 and to discuss are the following: the faunal change incident to the pas- 

 sage from the Bedford shale to the Berea sandstone; the Carboniferous 

 aspect of the Berea fauna, and its probable correlation with the Kinder- 

 hook of the Mississippi Valley; the Devonian aspect of the Bedford 

 fauna, and the relation of the Cuyahoga, Berea and Bedford faunas to 

 those of the typical Mississippian sections of Missouri, Illinois and Iowa. 



3 The typical sections of the Devonian and Carboniferous in the United States are 

 meant. The original sections are of course in Europe. 



4 This statement is based upon the fact that Hall described and included in the Che- 

 mung fauna numerous pelecypods from many of the well-known "Bradfordian" locali- 

 ties of Pennsylvania. 



5 Here and elsewhere in this paper, "Bradfordian" is employed in the sense in which 

 I defined it in 1904 (Science, N. s., vol. 19, p. 24) — for a series of strata about 500 feet 

 thick, lying between the typical Chemung and the Waverly group (as limited below by 

 the Berea sandstone), and comprising in the typical sections near Bradford, Pa., and 

 Olean^ N. Y., the formations described under the names of Cattaraugus, Oswayo and 

 Knapp. 



