8 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



sonboro limestone ^ of Screven County, Georgia, has a number of 

 identical species, among which certain Cerites and species of Strom- 

 hus are noticeable. Only one species so far is Imown to survive into 

 the Chipola marl, though with a better knowledge of the fauna 

 others would doubtless be identified. 



The Chipola marls ^ were first observed in the lower stratum at 

 Alum Bluff, Florida, by Langdon, who supposed them to be Miocene, 

 but richer and better preserved deposits were later discovered by 

 Capt. Frank Burns, of the United States Geological Survey, on the 

 banks of the Chipola Eiver a few miles away. These were later 

 more fully explored by the present writer and Mr. Joseph Stanley 

 Brown, of the survey, and their relation to the other adjacent 

 elements of the Tertiary column of the Gulf coastal plain accurately 

 determined.^ About 50 per cent of the species in the Chipola beds 

 are peculiar to them; of the others the larger proportion are com- 

 mon to the Tampa Orthaulax bed, while in the subsequent Oak Grove 

 sands about 24 per cent of the Chipola species survive. A species 

 of Orthaulax different from those of Santo Domingo and the Tampa 

 silex beds is found in the Chipola, after which the genus disappears 

 from our Tertiary. 



The Oligocene marl of Bowden, Jamaica,* formerly supposed to 

 be Miocene, is naturally more nearly related to the Oligocene of 

 Haiti and Santo Domingo, but contains many Chipola species. It 

 is certain that Gabb's collection from Santo Domingo contains ma- 

 terial from more than one horizon. One of the zones, however, 

 must be contemporaneous with the Orthaulax bed since the charac- 

 teristic species occur in both. Part of the rest is doubtless younger 

 and may even prove Pliocene, a confusion which can only be cleared 

 up by further stratigraphical study. The Bowden fauna does not 

 contain Orthaulaoc^ though it has many Chipola species, and its 

 relations are probably with the series between the Chipola marls and 

 the Oak Grove sands. 



The Oak Grove sands ^ were discovered at Oak Grove, Santa Rosa 

 County, Florida, by Mr. L. C. Johnson, of the United States Geo- 

 logical Survey, and later explored by Prof. E. A. Smith and Captain 

 Burns. They contain a well preserved and very interesting fauna, 

 which begins to show traces of the influences w^hich formed the sub- 

 sequent true Miocene. Subsequent explorations by Mr. T. H. 

 Aldrich, and Dr. T. Wayland Vaughan of the United States Geo- 

 logical Survey, have brought to light on Shoal River at no great 

 distance certain fossiliferous marls, which contain an analogous 

 fauna, probably of little difference in age. From Alum Bluff on 



iDall and Harris, Bull. U. S. Geol .Survey, No. 84, p. 73, 1892. 



- Trans. Wagner Inst., vol. 3, p. 1574. 



3 Bull. Geol. See. Amer., vol. 5, pp. 147-170, 1894. 



* Trans. Wagner Inst, vol. 3, p. 1580. 



^Idem., p. 1588. 



