INSTITUTE OF SCIENCE, PHILADELPHIA. 12l 



allowances for imperfections and deficiencies, it would still be impossible 

 to determine whether the percentage of recent forms ought rather to be 

 increased or diminished, unless a critical re-examination of all the species 

 were entered into. It is, however, a significant fact, that the percentage, 

 as determined by geologists who preceded Mr. Gabb, is placed very 

 much lower than by Gabb himself. Thus, by Guppy the proportion is 

 reduced to 20 per cent,, and by Carrick Moore to from 17 to 8 or 9 per 

 cent. (Q. Journ. Geol. Soc. London, xxii, p. 577). Mr. Guppy further 

 recognizes the proportion of living forms among the Jamaican fossils, 

 nearly all of which are stated by Gabb to occur also in Santo Domingo, to 

 be likewise 20 per cent., but in all these cases the material upon which 

 the determination was made was much less complete than that which 

 served as a basis for Gabb's computation, so that not unlikely the latter's 

 figures are more nearly correct than those furnished by his predecessors. 

 Granting the accuracy of Mr. Gabb's conclusions, the Santo Domingo 

 formation would then seem to represent a horizon somewhat higher in 

 the Miocene scale than is represented by the Florida deposits, in which, 

 as has already been shown, the proportion of recent forms is reduced to 

 13-15 per cent. This conclusion is in a measure borne out by the com- 

 paratively limited number of forms that are held in common by the two 

 series of deposits, a fact significantly emphasized when the proximity to 

 each other of the two areas under discussion is taken into consideration. 

 Still, it is not safe to premise on too scanty material, and while it may 

 be admitted without reservation that the silex-bearing deposit of Ballast 

 Point is of Miocene age, its exact horizon in the Miocene scale may be 

 considered to be as yet undetermined, although the strong probability 

 points to its representing a part of the " Virginian " series. It is surprising 

 that so few of the distinctly Miocene fossils of the Atlantic border should 

 be found here, the more especially as on the Big Manatee River, not more 

 than some thirty miles distant (almost due south), such fossils Pccten 

 Madisoniiis , Pccten Jcff'crsoiiins, Venus alveata, etc. are prominent by 

 their abundance. 



The fact that the silex-bearing deposit of Ballast Point can be 

 shown to be unequivocally of Miocene age is important as bearing 

 directly upon the age of the foraminiferal rock occurring at the same 

 locality, and at Magbey's Spring, about a quarter of a mile above Tampa, 

 on the Hillsboro River. It will be remembered that this rock was cor- 

 related by Conrad with the white limestone of the Vicksburg (Oligocene) 

 group, and merely from the circumstance of its containing in abundance 

 the remains of a foraminifer, supposed to be a nummulite (Nummulites 

 [Assilina] Floridanus). This supposed nummulite is, however, no nummu- 

 lite at all, but an orbitolite, so that whatever inference may have been 

 drawn from the occurrence of a form considered to be nearly related 



