CORRELATION OF THE TERTIARY FORMATION 621 



12a. Barbadian Eidge: As Barbados is connected undersea with To- 

 bago Island by a ridge less than 1,000 fathoms deep, and as the depth 

 between it and Saint Lncia is less than 1,000 fathoms, there is a closed 

 basin over 1,000 fathoms deep between the Barbadian Eidge and the main 

 Caribbean Arc. 



121). Caribbean Arc : The Caribbean Arc is a ridge that extends from 

 north of the Gulf of Paria to Anegada Passage. The islands occurring 

 along it from the Grenadines to Dominica are entirely or predominantly 

 volcanic. Guadeloupe is a compound island; the western half is volcanic; 

 the eastern half, with the outlying Marie Galante, is mostly composed of 

 calcareous sediments. North of Martinique the arc splits ; along the inner 

 fork are the volcanic islands Montserrat, the members of the Saint Chris- 

 topher Chain, and Saba ; along the outer fork are Antigua and Barbuda, 

 and the Saint Martin group. The latter islands are largely or predomi- 

 nantly composed of sedimentary rocks resting on an igneous basement of 

 pre-Tertiary or early Tertiary age. 



12c. Aves Eidge: This ridge takes its name from Aves Island, which 

 stands on a ridge running from the north coast of Cumana to Saba Island 

 at depths slightly less than 1,000 fathoms, while water of greater depth 

 occurs both east and west of it. 



Correlation of the Tertiary Formations of the south Atlantic 

 AND eastern Gulf Coastal Plain 



The accompanying table indicates the present status of the correlation 

 of these formations, and, although it may have to be modified to accord 

 with the results of additional investigations, there is every reason to be- 

 lieve that subsequent changes will be only in matters of minor refinement. 

 However, I wish to say that I believe four paleontologic zones will be 

 discriminated and defined in the Chattahoochee formation, and that the 

 collections on which to base these subdivisions have already been made 

 and in large part described, but I will not take the time to discuss these 

 details. I also confidently expect the Ocala limestone to be subdivided 

 into two or more zones, for the genus Orthophragmina, so abundantly 

 represented in the lower part of the formation, appears to be absent in 

 the upper beds. 



Correlation of the Tertiary sedimentary Formations of Panama 

 AND the West Indies 



A summary of these correlations is given on the accompanying table. 

 Only one point appears to need special comment — that is, whether the 



