22 THE EOCENE DEPOSITS OF MAEYLAND 



the other members of the series. It was seen that only by an under- 

 standing of the broad conditions affecting the whole district conld the 

 strata of any one formation be properly interpreted. Eeeognizing this 

 fact, the writers present in later pages a brief discussion of the general 

 relations of the strata composing the Coastal Plain in the Middle At- 

 lantic Slope. The fuller discussions will be found in the, later volumes 

 dealing with these formations. 



When we come to consider that assemblage of deposits (Eocene and 

 Neocene) early separated as the Tertiary, we find that it is divisible into 

 several distinct formations. Even at a relatively early date an older and 

 a younger Tertiary were already established, the former being corre- 

 lated with the Eocene of England and the European continent. At- 

 tempts were made then and later to find its exact equivalent in one or 

 another of the already established local formations of the English or 

 continental series, but with very unsatisfactory results. 



After the American Eocene strata had received somewhat detailed 

 examination in the various sections of the country and local divisions 

 had been established, attempts were made from time to time to deter- 

 mine their equivalenc}''. By common consent the diversified and exten- 

 sive deposits of the Gulf area came to be regarded as the type for the 

 eastern border region, and the various Eocene deposits of the Atlantic 

 Coast States were assigned to positions in this series. Some authors, 

 recognizing the presence of a few identical species, have referred the 

 strata now under consideration to a single minor division in the scale, 

 while others have regarded the Maryland-Virginia deposits as repre- 

 senting a larger portion of the Gulf series. After a careful consideration 

 of both the paleontological and the geological data, the writers deem 

 the latter conclusion the only tenable one. 



Attention has been devoted in the past too exclusively to supposed 

 faunal similarities, upon the most insufficient knowledge of the forms, 

 and too little to the character of the sedimentation. Important as the 

 former are when the fauna has been fully investigated, and the Avriters 

 . would be far from disparaging that importance, yet the widely different 

 physical conditions surrounding the accumulation of the deposits in the 

 two areas must at the same time be regarded. Chano-e in a fauna is 



