422 PROCEEDINGS OF THE ACADEMY OF [1898. 



ence of this fauna to the Upper Miocene — and we know that the ex- 

 tinct species [A limula and A. lineolata] are not quaternary even in 

 Florida — so, subject to the above assumption, I think we shall have 

 to regard it as Pliocene. * * * * The Croatan beds are dis- 

 tinctively Pliocene, but these are more like the contact between the 

 southern Pliocene and a more northern cold water fauna." 



Corroborative of the views already advanced as to the age of this 

 bed is the following, written by Prof. N. S. Shaler respecting the 

 mollusks listed above from near the Jericho Canal : " The species 

 determined by W. H. Dall, paleontologist of the U. S. Geological 

 Survey, indicates in a general manner that the beds are of Pliocene 

 age. Of the 29 species that appear in my collection, 24, according 

 to Dr. Dall, belong to living forms and 5 are extinct. The extinct 

 species are found in the so-called Pliocene of Florida, South Car- 

 olina and Virginia. There can be no question the deposit is of pre- 

 glacial age." 5 



We now consider the evidence presented by the diatom flora 

 which we think corroborates that presented by the mollusks for rea- 

 sons which we shall note after the introduction of the following state- 

 ment by Charles S. Boyer, A. M., Made by him after a careful ex- 

 amination of a number of mounts prepared from the material which 

 had been reliably cleaned, as already stated, by John A. Shulze, and 

 to which we are well assured there has been no admixture of di- 

 atoms from any other source : — 



"The following list includes all the forms, 31 in number, found 

 in the slides of the Dismal Swamp material except a few fragments 

 which were too small for accurate determination. 



"In the middle column is noted the relative frequency and rarity 

 of some of the forms in comparison with the rest as seen in the 

 strewn mounts : — 



" Of the above forms all but four are strictly marine. The ex- 

 ceptions are Navicula major and Stauroneis Phoenicenteron, which 

 are fresh water, Campylodiscus Echeneis which is both brackish and 

 fresh water, and Melosira crenulata var. antique/,, which is possibly 

 also fresh water. 



" I think I have named all on the slides at hand, except probably 

 one or two forms of Coscinodiscus and Navicula, which were in frag- 

 ments. 



5 Tenth Annual Report, U. S. Geol. Survey, page 315. 



