606 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



while St. Croix, which is closely related in its geologic features 

 to the Virgins, was probably at one timo a member of that 

 group and has been separated from them by faulting of compara- 

 tively late geologic date. There is no direct evidence of the 

 existonco at this time of any of the Caribbean Islands, but certain 

 relations suggest that at least parts of the Caribbean Arc maybe old. 

 St. Croix stands on the western end of a ridge botweon 600 and 700 

 fathoms deep, on the eastern end of which is St. Christopher. This 

 ridge extends northward to the St. Martin Plateau, eastward to 

 Antigua and Barbuda, and southward from the latter islands through 

 Guadeloupe, St. Lucia, and the Grenadines to South America. 

 These relations suggest that tho eastern perimeter of tho Caribbean 

 Basin may have been outlined in late Paleozoic time. 



From the preceding statement it is evident that the principal 

 tectonic lines of the perimeters of the Gulf of Mexico and Caribbean 

 Sea existed at the close of the Paleozoic. The northern, western, 

 and southern boundaries had been outlined and the major transverse 

 trends had also been formed, the more northern through Oaxaca 

 and Chiapas, including the northward trending Coxcomb Mountains 

 of British Honduras; the more southern through Honduras and 

 Nicaragua. The first may have connected along the axis of the 

 Coxcomb Mountains with Cuba and thence Haiti; the second prob- 

 ably connected with Jamaica, Haiti, Porto Rico, and the Virgin 

 Islands, and there are vague suggestions that the Caribbean Arc 

 also existed. As the positive and negative areas so early outlined 

 dominated the tectonic development during later geologic time, the 

 subsequent history consists in tracing the modification of these old 

 features. 



TRIASSIC, JURASSIC, AND CRETACEOUS. 



It seems necessary to infer diastrophic movements previous to or 

 during Jurassic and Cretaceous time, for there was no connection 

 between the Atlantic and Pacific oceans across Central America dur- 

 ing these periods, with the possible exception of certain connections 

 during Jurassic and upper Triassic (Karnic) time, as shown in the 

 table on page 612. During Triassic and Jurassic time the eastern part 

 of the North American continent, except areas of Triassic in Mexico 

 and several Central American States and areas of Jurassic in Mexico 

 and trans-Pecos Texas, was emerged probably to the limits of the pres- 

 ent Continental Shelf, while the western end of Cuba was submerged. 

 The eastern end of Cuba apparently was a land area and may have 

 been joined to the southeastern United States. During upper Creta- 

 ceous time there was extensive submergence throughout the West 

 Indies and Central America, but the Lower Cretaceous, as represented 

 in Mexico and Texas, is not known in them, except in Honduras. 

 As the Jurassic and Cretaceous faunas are Atlantic in their facies, 



