GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 593 



It has already been stated that the fossils obtained by Miss Maury 

 in Santo Domingo at horizons higher than her zones G, H, and I are 

 younger than the Bowden fauna. A line of demarcation between 

 the Burdigalian and higher Miocene is not at present practicable, but 

 it is almost, if not quite, certain that her upper zones are not older 

 than Helvetian. This would still seem to indicate a horizon below 

 the lowest formation of the Chesapeake group of Maryland and Vir- 

 ginia and the Marks Head marl of eastern Georgia, but the available 

 data do not warrant a positive opinion. However, it appears that the 

 higher Miocene deposits of the Santo Domingan section are represented 

 in Florida and Georgia by the erosion interval between the deposition 

 of the uppermost beds of the Alum Bluff formation and that of the 

 overlying Marks Head marl. 



The presence in Cuba of deposits, the La Cruz marl, of the same 

 age as the Santo Domingan deposits above Miss Maury's zones H-I, 

 was noted on page 219 of this volume. 



It seems that there are in the southeastern United States no Miocene 

 marine deposits of the same age as the upper part of the Gatun 

 formation, the Santo Domingan deposits above Miss Maury's zones 

 H-I, and the La Cruz marl of Cuba, unless some of the latter deposits 

 are younger than is at present supposed. 



Except for the Isthmus of Tehuantepec, there is no information on 

 marine Miocene formations of this age in eastern Mexico, or in the 

 area between Yucatan and Costa Rica. The extension of the Gatun 

 formation into Costa Rica has already been discussed. 



PLIOCENE. 



The Toro limestone is the only formation within the Canal Zone 

 that is supposed to be of Pliocene age. The determination of the 

 age of this formation is necessarily by means of its stratigraphic 

 relations, as only one identifiable species of fossil, Epitonium toroense 

 Dall, was collected in it, but the stratigraphic relations, described by 

 Doctor MacDonald on pages 544, 545 of this volume, are such that 

 the formation can scarcely be of any age other than Pliocene. 



The Pliocene deposits in the vicinity of Limon, Costa Rica, 

 were first observed by W. M. Gabb, 1 who described a number 

 of species from there, and they were later visited by R. T. Hill, 2 who 

 made additional collections, on which Doctor Dall supplies notes 

 published in the paper cited. 3 Doctor Dall has recently described 

 an interesting species of Pecten, P. pittieri,* collected b} T Mr. H. Pittier 

 at Moin Hill, near Port Limon. This species will be referred to in 



i Gabb, W. M., Descriptions of new species of fossils from the Pliocene clay beds between Limon and 

 Moen, Costa Rica, together with notes on previously known species from there and elsewhere in the Carib- 

 bean area, Acad. Nat. Sci. Philadelphia Journ., ser. 2, vol. 8, pp. 349-3S0, figs, on pis. 45-47, 1881. 



a Mus. Comp. Zofil. Bull., vol. 28, p. 234, 1898. 



8 The geologic history of the Isthmus of Panama and portions of Costa Rica, Mus. Comp. Zool. Bull. , 

 vol. 28, p. 274, 1898. 



« Smithsonian Misc. Coll., vol. 59, p. 10, 1912. 



