28 Cl BA AND POETO 1UCO 



chapter of this book. Its complicated geologic history, 

 and the facl that a Large portion of its extent is now sub- 

 merged beneath the ocean, are not the least interesting <>f 

 its many features. 



The Antillean uplift, as a whole, may 1><' compared to 

 an inverted, elongated canoe, the highest and central part 

 of which is in the region adjacent to the Windward Pas- 

 sage. Thus it is that the higher peaks occur in Haiti, 

 eastern Cuba, and eastern Jamaica, while the arching 

 crest-line descends toward the western part of the two 

 latter islands, and on the east toward Porto Rico, where 

 the highest summit is only 3680 feet, finally disappearing 

 as the Virgin Islands, where, in St. Thomas, the summit 

 is 1560 feet. 



The higher mountains are composed of non-calcareous 

 clay and conglomerate, largely the debris of unknown 

 lands of pre-Tertiary time, which, with the exception of a 

 few restricted points, were buried, during a profound sub- 

 sidence in early Tertiary time, beneath a vast accumulation 

 of calcareous oceanic sediments. The latter now compose 

 the white limestones which constitute the chief formations 

 of the islands, and which were, together with the preced- 

 ing formations, elevated into their present position at the 

 close of the Tertiary period. The mountains are irregu- 

 larly flanked below 2000 feet by horizontal benches, or 

 terraces, of this limestone, which are the result of regional 

 elevations and base-leveling after the last period of moun- 

 tain-making. There are also intrusions of old igneous 

 rocks, granitoid, porphyri tic, and basaltic, but these are 

 of a more ancient character than the volcanic rocks of the 

 Windward chain, and nowhere are there craters or other 

 traces of recent volcanic vents. The mountains above 

 2000 feet, composed'of the older non-calcareous formations, 

 and the lower plains and bordering plateaus of limestone, 

 result in producing the two distinct and contrasting types 

 of calcareous and non-calcareous soils throughout the 

 Great Antilles. 



