of the Middle Atlantic Coast Eocene. 371 



been regarded by some to represent a single minor division of 

 the Gulf section, while others have regarded them as an equiva- 

 lent of a larger portion of that series. The latter conclusion 

 seems to the writer, after a consideration of both the geological 

 and paleontological data, to be the only tenable position. In 

 the past too little attention has been given to the geological 

 phenomena, while, at the same time, the knowledge of the 

 fossils has been wholly insufficient for a proper interpretation 

 of the faunal characteristics of the formation. 



The Geological Criteria. — The lithological and stratigraph- 

 ical characteristics of the Eocene in the middle Atlantic slope 

 afford some important criteria for the correlation of the strata. 

 To begin with, the homogeneous nature of the deposits is a 

 characteristic feature, indicating conditions throughout the 

 period of Eocene deposition, undisturbed by important phys- 

 ical changes. Again, the fact that the strata are so largely 

 made up of secondary materials shows that the position of 

 accumulation was in the vicinity of a coast reached by no large 

 rivers bearing sediment, while at the same time sufficiently 

 removed from the coast line to be unaffected by shore condi- 

 tions. It is further evident that these deposits, which are so 

 largely glauconitic, were accumulated with exceeding slowness, 

 as has been shown in the case of the formation of greensands 

 upon the beds of existing seas. 



Now when we compare these conditions of accumulation in the 

 middle Atlantic slope with the conditions that prevailed in the 

 Gulf region, marked differences appear. In the latter area 

 numerous rivers, draining the interior of the continent, dis- 

 charged great quantities of material throughout much of Eocene 

 time, making the deposits highly diversified. Instead of the 

 green-sands and greenish and black clays of the middle Atlantic 

 slope, which no longer to any large extent characterize the 

 strata, are found coarser beds of sand and clay, often partly 

 calcareous, which give every indication of more rapid accumu- 

 lation. To compare, therefore, the 200 feet and more of green 

 sands and clays of the middle Atlantic slope with one or two 

 subdivisions of hardly equal thickness in the Gulf region 

 would, even upon stratigraphical grounds without the aid of 

 fossils, hardly be attempted. The strata of the Middle Atlantic 

 slope must be represented in the Gulf by deposits many times 

 their thickness. 



The general relations of the strata, occurring as they do 

 between the Cretaceous and Neocene along both the Atlantic 

 and Gulf coasts, give some indications of the continental move- 

 ments to which each province was subjected. Although the 

 movements may not have been absolutely contemporaneous 

 they afford nevertheless satisfactory criteria for the broad 

 correlation of the deposits, their more exact parallelism being 

 determined upon other grounds. 



