6 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



characteristic of his " Group " are not confined to the two horizons 

 represented in it, and can not, therefore, serve as tests of identity 

 or difference of faimal epochs. 



The name Peninsular limestone was proposed by the writer in 

 1903^ for the Orbitoidal limestone, which forms the mass of the 

 Floridian plateau and in which artesian wells have been sunk 

 through a distance of over 1,500 feet without reaching its lowest 

 limit. The statement is as follows: 



The Orbitoidal limestone which forms the mass of the Floridian plateau, and 

 which has been, in this work and in the literature, generally called the 

 " Vicksburg limestone," may really form a different horizon altogether from 

 the typical Yicksburgian and be intermediate between the latter and the Num- 

 mulitic Ocala limestone. In order to promote clearness and avoid confusion, 

 it is probably advisable to adopt a distinct name for the Orbitoidal phase or 

 formation for which I would suggest the term Peninsular limestone. This is 

 Intended not as a permanent formation name, but as a general term for the 

 fundamental plateau limestone of Florida, in which a close and thorough study 

 in the future may result in the discrimination of more than one horizon or 

 zone. 



An examination of all the molluscan fossils in the collection of the 

 United States National Musemn which have been obtained by the 

 United States Geological Survey from the Peninsular limestone shows 

 that of 19 species 13 are are peculiar to it and 4 are identical with 

 typical Vicksburg species. The limestone, except in its upper por- 

 tion where it merges into the Ocala or Nunmiulitic phase, is very poor 

 in fossils, except foraminifera, and only two or three of the mollus- 

 can fossils are at all common ; practically all of the conspicuous shells 

 of the upper horizon at Vicksburg have dropped out, a few of them 

 to reappear in the Ocala. The foraminifera have not hitherto had 

 the careful study they need, but are now in the hands of Dr. Joseph 

 A. Cushman for that purpose. There are two widely distributed 

 and rather common Echinoids, Pygorhynchus goiddii Bouve, and 

 OUgopygus haldermani (Conrad) Twitchell, neither of which has 

 been reported from Vicksburg. Dr. T. W. Vaughan, after extensive 

 explorations between the Mississippi and Savannah Elvers and in 

 northern Florida, is of the opinion that the Peninsular limestone 

 "can not be separated stratigraphically from Vicksburgian lime- 

 stones to the east and north," and that " no stratigraphic line can be 

 drawn between it and the overlying Ocala limestone." This is very 

 probable, but the distinctions sought to be drawn by the writer are 

 faunal or paleontological, not stratigraphic, since experience has 

 shown that only by their contained faunas can the different and 

 relative ages of these excessively similar successive limestones be 

 finally determined. In the present case the Ocala phase or zone af- 

 fords 59 species of mollusks, of which 25 are peculiar to it (as far as 



1 Trans. Wagner Inst., vol. 3, p. 1554. 



