FAUNA OF ORTHAULAX PUGNAX ZONE. 15 



This genus of Foraminifera appears to replace LepidocycUna (bet- 

 ter known as Orhitoides in this country) in these two horizons. 



The molhiscan fauna of the limestone immediately above the silex 

 beds has not been thoroughly studied, but it is notable for the num- 

 ber of Cerites contained in it and for the profusion of Orhitolifes 

 fioridanus Conrad (? corri'planatus Lamarck), and it seems allowable 

 to apply the name of the latter species as a designation of this zone, 

 with the type-locality at Ballast Point. 



The fauna represented in the lower bed at Alum Bluff, on the 

 Chattahoochee River, Florida, and in the Chipola marl has been 

 fully though not exhaustively treated in the writer's work on the 

 Tertiarj Fauna of Florida.^ It is a remarkably rich and beautifully 

 preserved fauna, containing one species of Orthaulax {0. gahhi 

 Dall), the last representative of the genus in our Tertiarj^ It is 

 also notable for the abundance of a bivalve, Cardimn cesium Dall, 

 the name of which I have selected to designate the zone typified by 

 the fauna of the Chipola marl at the locality on the Chipola River 

 near Bailey's Ferry, Calhoun County, Florida. 



These three zones form a natural f aunal group, characterized by 

 a large proportion of common species, by indications of uniform cli- 

 matic conditions bordering on the tropical, and by the presence of 

 peculiar genera not existing in the faunas succeeding to them. 



The next superior zone, of which the fauna is fairly well laiown, 

 though in part unpublished, is that referred to by the writer in 1892, 

 as represented by the Alum Bluff beds and the sands at Oak Grove, 

 Santa Rosa County, Florida. This horizon is conspicuously dis- 

 tinguished by the greenish or grayish color of the matrix as compared 

 with the yellow or orange of the zone below, by the disappearance of 

 Orthaulax and many of the more distinctively tropical forms from 

 the fauna (though a fair proportion of Chipola forms still remain) , 

 and by the appearance in the fauna of a certain number of types 

 prefiguring the cold-water fauna which accompanied the deposition 

 of subsequent beds of Miocene age. 



The type-locality is at Alum Bluff where the strata lie above the 

 marl of the Chipola type at the base of the bluff, and contain few 

 if any fossils, while the Miocene lies directly alcove them. But the 

 horizon was traced continuously to Rock Bluff by the writer and Mr. 

 J. Stanley Brown of the United States Geological Survey in 1893. 



At Rock Bluff it contains characteristic littoral species which con- 

 nect the fauna unmistakably with that of the Oak Grove sands which 

 contains a large number of well-preserved species belonging in deeper 

 water. One of the most characteristic of these, Scaj)harca dodona 

 Dall, is present in large numbers and may be used to designate the 

 zone. 



1 Trans. Wagner Inst, vol. ?., 1890-1903. 



