620 T. AV. VAUGHAN GEOLOGIC HISTORY OF CENTRAL AMERICA 



86. Saint Croix: Although Saint Croix is separated from the Virgin 

 Islands by a depth as great as 2,400 fathoms and is joined to the Saint 

 Christopher chain by a ridge less than 1,000 fathoms deep, it possesses 

 great similarity to members of the Virgin group. The west end is trmi- 

 cate and the submarine slope precipitous; the submarine slope to the 

 north is also steep. There is clear evidence of faulting on the west and 

 north sides. A ridge, largely of igneous rock, stands against the north 

 shore from the west end of the island for some distance to the east. South 

 of the ridge is a sloping, rolling, calcareous plain. The east end has a 

 submarine continuation in a bank less than 50 fathoms deep. The tec- 

 tonic axis is east and west, the rocks resemble those of the Virgins, and 

 the zeogeography indicates former connection with them. For these rea- 

 sons it seems probable that this island was formerly a part of the Porto 

 Rican-Virgin Island land-mass and has been sundered from it by dias- 

 trophic processes. However, Saint Croix might be accorded separate 

 status as a province, or referred to the Saint Christopher axis ; but it ap- 

 pears to me preferable to classify it with the Virgin Islands. 



9. Costa Rica-Panama : Between the Mcaragua-Costa Rican boundary 

 and the mouth of Rio Atrato is an S-shaped land area which does not ex- 

 hibit striking tectonic lines, although some deformation axes are obvious 

 in Panama. The region is largely one of vulcanism, present or past, 

 which, although occurring within limits, does not follow continuous 

 straight axes, but occurs in a curving belt. The topography appears dis- 

 ordered, with volcanic protuberants here and there without perceptible 

 system. The volcanic heaps range from a few hundred to nearly 10,000 

 feet in altitude. 



"10. Andes: The south-north trending ranges of the Andes reach the 

 shores of the Caribbean Sea between the gulf of Darien and Venezuela, 

 and send a spur, Cordillera de Merida, northeastward to 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 of Curacao, Arube, and Bonaire lie off the Venezuelan 

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

 de Merida. 



11. Maritime Andes: The Maritime Andes lie along the Venezuela 

 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. 



