210 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



The most important result of this subsidence was the fact that it sub- 

 merged the Isthmus of Panama, and again permitted shallow connection 

 between the great oceans, as I have shown in my report upon that region, 

 — a passage which was temporarily closed shortly afterwards. All the 

 known evidence, as presented in my recent report, tends to show that 

 this passage was shallow and ephemeral. This is the only epoch in 

 geologic history between the Cretaceous and the present in which there 

 is evidence of this passage having been open. 



Succeeding this Tertiary subsidence was the chief of the great erogenic 

 movements which built up the east and west folds of the Antillean moun- 

 tain systems as now occurring directly across the paths of the pre-exist- 

 ing Andean and Eocky Mountain trends. This undoubtedly was the 

 most important relief producing event in all Antillean history ; to it 

 much of the present configuration of the land and sea bottom is 

 due. The whole configuration of the Antillean lands, the western Carib- 

 bean floor, the northern shore of South America, and the Central Amer- 

 ican lands were revolutionized by the development of these corrugations, 

 accompanied by igneous action, including great laccolithic intrusions of 

 igneous rocks. 



Seebach ^ long since pointed out the now accepted conclusion that the 

 North American Cordilleras terminate with the " Abfall " of the Mexican 

 Plateau, and showed the distinction between it and the entirely oppo- 

 site erogenic trends in Central America and the Antilles. Suess, in his 

 masterly compilation,^ has still further demonstrated the existence of 

 these trends, but owing to inaccuracies of the current geologic data he 

 grouped the phenomena somewhat differently from the manner in which 

 I would arrange them, having connected under the name of the Cor- 

 dillera of the Antilles the true Antillean trends with those of the 

 Caribbee chain. This, in my opinion, is not an harmonic arrangement. 

 According to the elaborated strikes later platted by Sievers,^ the Bar- 

 badian, Grenadan, and Aves Island ridges of the Windward bridge, at 

 least in its southern half, are more in line with his " Carribischen " 

 ranges of the north coast islands of South America than with the 

 Antillean chain. These uplifts, collectively, now constitute a series of 

 many chopped up, parallel east and west ridges, which have been greatly 

 disconnected and partially submerged by subsequent events, but of 

 which many distinct ranges may still be identified. The most north- 

 ern of these are the Segovian trends of Oaxaca, Chiapas, Guatemala, and 



^ Epitomized by Dollfuss and Mont-Serrat. 



2 Das Antlitz der Erde, Chapter X. pp. 698-702. 



« Petermann's Mitteilungen, Vol. XLII., 1896, Part 6. 



