1898.] NATURAL SCIENCES OF PHILADELPHIA. 427 



It has also been found fossil by Prof. C. S. Boyer, in specimens of 

 clays obtained by the writer from tbe upper portions of two well 

 borings, one on the beach at Wildwood, 7 Cape May Co., N. J., and 

 the other at Rock Hall, 8 Md., on the eastern side of Chesapeake 

 Bay opposite the mouth of the Patapsco river. The clays referred to 

 occupied, at Wildwood, the interval between the depths of 79 and 

 181 feet, and at Rock Hall a similar interval between the depths of 

 50 and 130 feet. The clays at both localities contained a mixture 

 of fresh-water and marine diatoms, the numbers of individuals of the 

 fresh-water forms somewhat exceeding those of the marine. That 

 these two deposits are probably synchronous in age appears probable 

 from the similarity of their position next below the surface forma- 

 tion (Cape May formation ?), also from the similarity of the as- 

 sembled forms of diatoms, and from the occurrence in both of a 

 unique diatom, Polymyxus coronalis, L. W. Bailey, not however, found 

 in our examination of the forms in the Dismal Swamp bed. This 

 form has not been heretofore known except as living off the mouths 

 of the Para and Amazon Rivers in South America. That the two 

 deposits are much later than Miocene in age may be inferred from 

 the fact that the one at Rock Hall lies directly upon the Rancocas 

 division of the Cretaceous, the Miocene itself resting at a higher 

 level upon Eocene beds a few miles southward and eastward ; while 

 at Wildwood the top of the great Miocene diatom clay bed occurs 

 nearly 200 feet deeper than the base of the deposit under considera- 

 tion, or at the depth of 370 feet from the surface. The well borings, 

 however, show that apparently the same Miocene clay, but without 

 diatoms, commences at the depth of 294 feet. 



These two deposits containing Polymyxus coronalis and Stauroneis 

 Phoenicenteron, the writer suggests were probably laid down in the 

 deltas of the ancient Delaware and Chesapeake Rivers at the time 

 when the shore line of the Atlantic Coastal plain was many miles 

 eastward of its present position and much of the now submerged 

 portion of the plain was above sea level. 



SUMMARY. 



After considering the position of the Dismal Swamp bed, beneath 

 a low lying terrace on the eastern margin of the Coastal Plain and 

 evidently resting immediately upon fossiliferous Miocene beds which 



T An. Report Geol. Survey of N. J. for 1894, page 165. 

 8 In manuscript, not yet published. 



