586 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



Recently Dr. Sidney Powers has presented to the United States 

 National Museum some specimens ho collected at the entrance to 

 Rio Dulco, Guatemala. The rock is a massive light-colored,, fine- 

 textured limestone, with a conchoidal fracturo, and contains many 

 poorly preserved fossils. Among the fossils aro Orbiiolites species; 

 several corals, one of which resembles Siderastrea, another is probably a 

 specimen of Goniopora, and a third seems to bo a branching poritid 

 coral that looks precisely like a coral obtained by Doctor MacDonald 

 in limestone, referred by him to tho Emporador limestone, in the 

 swamp north of Ancon Hill and about one-quarter of a mile south 

 of Diablo Ridge, Canal Zone; and there aro specimens of Osirea, 

 Peclen, and Lima. This material is too poor to warrant a positivo 

 opinion, but it is worth noting, and it probably represents a hori- 

 zon very near that of the Emporador limestone. 



According to Hill's account of the stratigraphic succession in 

 Jamaica, the correlatives of those uppermost Oligoceno deposits aro 

 represented there by a stratigraphic break, the unconformity be- 

 tween the Montpclier white limestone and the Bowdcn marl. 



MIOCENE. 



The definite correlation of the Canal Zone Miocene with European 

 horizons was first attempted by H. Douville in his paper, already 

 cited, on the age of the deposits along the Panama Canal. He 

 says regarding the deposits overlying those discussed in the fore- 

 going remarks: "Leur age est incontcstablcmcnt Miocene." 1 He 

 considers the lower part of theso deposits as Burdigalian, the upper 

 part as Helvetian in age. That part of tho Gatun foimation exposed 

 at Monkey Hill is referred to the Helvetian. 



The literature on the age of the Gatun formation is considerable, 

 but a lengthy review of it appears unnecessary. The papers by 

 Toula and by Pilsbry and Brown have already been cited on page 

 560 of this volume. Actually there is in most cases more apparent 

 than real discrepancy between the correlations of the different 

 investigators, due to tho fact that tho Alum Bluff formation, includ- 

 ing the Chipola marl member at its base, has been referred to the 

 upper Oligocene. The Alum Bluff formation is certainly of Miocene 

 age, according to European usage, and is tho American equivalent 

 of the Burdigalian. All available evidence indicates that the lower 

 part of the Gatun formation in the Canal Zone is the equivalent of 

 the Alum Bluff formation of Florida and Georgia. Although tho 

 Gatun formation contains numerous species of Foraminifcra, echi- 

 noids, and Crustacea, the fauna is predominantly molluscan, and tho 

 discrimination of zones within it must await tho completion of the 

 study of the careful zonal collections Doctor MacDonald and I 



1 Soc. Giiol. France Hull., vol. 26, p. 599, 1898. 



