GEOGRAPHIC RELATIONS OF THE THREE AMERICAS 617 



Twelve major tectonic provinces, with several subordinate provinces, 

 may be discriminated, as follows : 



1. Bahamas. 



2. Atlantic and Gulf Coastal Plain. 



3. Mexican Plateau. 



4. Oaxaca-Guerrero. 



5. Yucatan. 



6. Guatemala-Chiapas. 



7. Cuba and northern Haiti. 



8. Honduras and its continuation to Jamaica, southern Haiti, Porto 



Rico, the Virgin Islands, and the outlying island of Saint Croix. 



9. Costa Rica-Panama. 



10. Andes. 



11. Maritime Andes. 



12. Caribbean Islands. 

 12a. Barbadian Ridge. 

 12?). Main Caribbean Arc. 

 12c. Aves Ridge. 



Of these provinces, (1) the Bahamas, (2) the Atlantic and Gulf 

 Coastal Plain, and (3) the Mexican Plateau will be only mentioned, but 

 the others will be briefly described. 



4. Oaxaca-Guerrero : A structural axis extends through Michoacan, . 

 Guerrero, and Oaxaca, almost at right angles to the trend of the Mexican 

 Plateau. The northern boundary of this province is the escarpment at 

 the southern margin of the Mexican Plateau; the western and southern 

 boundary is the Pacific Ocean, while the eastern boundary is the Isthmus 

 of^Tehuantepec. It is thus set off from the Mexican Plateau and the 

 Yucatan lowland. 



5. Yucatan: This province consists of lowlands under 600 meters in 

 height, underlain by only slightly deformed Tertiary strata, except some 

 problematic rocks west of Belize. ; The Yucatan Peninsula and Campeche 

 Bank are comparable to the Floridian Plateau. They are developed along 

 a structural axis almost at right angles to the continental trend. Cam- 

 peche Bank projects northward from the shoreline of the peninsula 170 

 nautical miles to the 100-fathom curve, and has a width of nearly 360 

 nautical miles along an east and west line. On the east the depth of 

 water between it and Cuba exceeds 1,000 fathoms and the axial trends 

 are not coincident, but the axis of Yucatan Bank and that of the Province 

 of Pinar del Rio, Cuba, curve so that they are nearly parallel, with a 

 trough, Yucatan Channel, between them. 



6. Guatemala-Chiapas: This province lies between the Yucatan low- 

 land on the north and Rio Motagua on the south. It is an upland domi- 



XLVI — Bull. Geol. Soc. Am., Vol. 29, 1917 



