302 ANNALS NEW YORK ACADEMY OF SCIENCES 



can often be referred to a genus with certainty while its specific position 

 is a matter of doubt. On the other hand, a provisional specific identifi- 

 cation is sometimes only possible on the assumption of a generic one. 

 Though because of their more extended range (in part compensated by 

 the certainty of delimitation), the larger groups are less serviceable in 

 correlating different sections, they are more instead of less valuable in 

 estimating the importance of faunal changes in the same section, since 

 they indicate a greater degree of change and possess the added advantage 

 of increased certainty of discrimination. 



Of equal importance with identification of a form in its biologic rela- 

 tions is the identification of its geologic horizon and this is frequently 

 unsatisfactory. It seems to be true, and it is natural that it should be 

 so, that in geologic time, as at the present day, the progress of sedimenta- 

 tion and the course of biologic development varied in different areas or 

 provinces, and that deposits may be, so far as one can tell, essentially 

 contemporaneous, and yet very different in lithologic character and in 

 the character of their fauna and flora. The limits of geologic provinces 

 are not clearly defined, if indeed it is not ultimately shown that they are 

 without definite limits but are continuous with one another; and still 

 less is it known what were the factors which produced their differentia- 

 tion. For my own part, I have very little faith in the theory of barriers 

 (in the sense of land barriers) as a panacea for all the ills of strati- 

 graphic geology. On the contrary, I believe that during geologic time, 

 as today, the conditions controlling the character and distribution of 

 faunas are depth, temperature, food supply, current action, salinity, bot- 

 tom and so forth. At all events, as between different provinces, most 

 correlations are at present more or less provisional, so that while the 

 paleontologist must not disregard the data from any area, his deductions 

 concerning one province should be largely guided by the data from that 

 province. 



Since the data of range and distribution of species are in large meas- 

 ure not on record even when they have been ascertained, and since the 

 records are very scattered, each investigator must approach a problem 

 with a different store of facts on which to base his inference as to geo- 

 logic age and correlation, but it by no means need follow that such partial 

 or even one-sided knowledge must lead in different cases to different 

 conclusions. 



A number of years ago when much engaged with the investigation of 

 these "Bradfordian" beds, from which I have since been temporarily 

 diverted, I began and all but completed a descriptive study of the fauna 

 of the "Corry" sandstone (since correlated with the Berea sandstone). 



