604 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



Porto Cabello where the main Andean trend is crossed by that of the 

 Maritime Andes. The shore of the Caribbean Sea lies across the 

 northern end of the Andes in a way similar to the manner in which 

 the landward border of the Coastal Plain crosses the southwestern 

 end of the Appalachian Mountains. 



The islands Curacao, Arube, and Bonaire, lie off the Venezuelan 

 coast in the angle between the ends of the main Andes and tho 

 Cordillera de Merida. 



11. Maritime Andes. — The Maritime Andes lie along the Vene- 

 zuela coast from Caracas eastward. Trinidad and Tobago are 

 outlying islands. On the south side of these mountains is the great 

 Valley of the Orinoco. 



12. Caribbean Islands. — These islands lie along triple arcuate 

 ridges, the Barbadian Ridge, the main Caribbean Arc, and Aves 

 Ridge, the second of which is double at its northern end. 



12a. Barbadian Ridge. — As Barbados is connected undersea 

 with Tobago Island by a ridge loss than 1,000 fathoms deep, and 

 as the depth between it and St. Lucia is less than 1,000 fathoms,, 

 there is a closed basin over 1,000 fathoms deep between the Bar- 

 badian Ridge and the main Caribbean Arc. 



12&. 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. Guadaloupe 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 

 St. Christopher Chain, and Saba; along the outer fork are Antigua 

 and Barbuda, and the St. Martin group. The latter islands are 

 largely or predominantly composed of sedimentary rocks resting on 

 an igneous basement of pre-Tertiary or early Tertiary age. 



12c. Aves Ridge. — 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. 



Paleographic Summary. 



There are many publications dealing with this subject, some of 

 which, such as those of Gregory, 1 Hill, 2 and Guppy, 3 are specially 



i Gregory, J. W., Contributions to the paleontology and physical geology of the West Indies, GeoL 

 Soc. London Quart. Journ., vol. 51, pp. 255-310, pi. 31, 1S95. 



2 Hill, R. T., Notes on the geology of Cuba, based upon a reconnaissance made for Alexander Agassiz, 

 Mus. Comp. Zool. Bull., vol. 16, pp. 2-13-288, pis. 3-9, 1895; The geological history of the Isthmus of Panama 

 and partions of Costa Ri:a, Idem., vol. 28, pp. 159-2S5, pis. 1-19, 1S98; The geology and physical geography 

 of Jamaica, Idem., vol.31, pp. 1-226, 252-255, pis. 1-35, 1901; Pe!<5and the, evolution of the Windward Archi- 

 pelago, Geol. Soc. Ameri a Bull., vol. 16, pp. 243-288, pis. 43—17, 1905. 



s Guppy, R. J. L., The gaologisal connexions of the Caribbean region, Canada Inst. Trans., vol. 8, pp. 

 373-391, one plate, 1909. 



