NATURAL AREAS AND REGIONS 



701 



in the Sierra de Luquillo in the eastern 

 portion; this cretaceous mountain axis, 

 broken and reaching much lower eleva- 

 tions, forms the Virgin Islands to the 

 east, the crown of St. Thomas being 

 about 1500 ft. altitude, the hills of St. 

 Jan about 1300 ft. Tortola about 1600 

 ft.; Virgin Gorda perhaps 1400. St. 

 Croix reaches about 1250 ft. on the 

 summit of Mt. Eagle. 



East of the Virgin Passage the islands 

 of St. Thomas; St. Jan; Tortola and 

 Virgin Gorda have many dependent 

 bays and islets forming altogether the 

 most beautiful archipelago within the 

 American tropics; the marine views 

 from the hills are wonderfully attractive 

 and the climate is most enjoyable. 

 Anegada, the most eastern of the archi- 

 pelago, is a low aeolian limestone and 

 sand island, with considerable differ- 

 ences from all the others in its plant 

 and animal population. St. Croix lies 

 some miles south of the rest of the 

 archipelago and is also somewhat differ- 

 entiated biologically. 



Lying unconformably on the upturned 

 edges of these cretaceous strata on the 

 northern and southern sides of Porto 

 Rico, except eastward, are Tertiary 

 shales and limestones locally heavily 

 fossiliferous, often cavernous, only 

 slightly tilted, deeply eroded into char- 

 acteristic peaked hills and mountains, 

 with many vertical escarpments; these 

 limestones attain great thickness in 

 western Porto Rico, thinning out east- 

 ward and seen only as isolated hills 

 and finally disappearing toward the 

 eastern end of that island and not rep- 

 resented at all in the Virgin Islands 

 from Culebra eastward; on St. Croix, 

 however, these Tertiary strata underlie 

 large areas. 



The distribution of rainfall is widely 

 unequal in different parts of the prov- 

 ince, and especially in Porto Rico, 

 and is the most potent factor in the 

 natural distribution of plants. It is 

 greatest in the northeastern mountains 

 of the Sierra de Luquillo and in the 

 Cordillera Central, and least in the 



southwestern parts of Porto Rico, where 

 desert conditions obtain, characterized 

 locally by the abundant growth of 

 several species of cacti and numerous 

 other xerophytic types. 



B. POLITICAL RELATIONS AND 

 COMMUNICATION 



Porto Rico; St. Croix (Santa Cruz); 

 St. Thomas and St. Jan are United 

 States Islands. Tortola, Virgin Gorda 

 and Anegada are British. 



Porto Rico includes politically the 

 island dependencies Mona and Desecheo 

 to the west in the Mona Passage; Cayo 

 Muertos off the southern coast; Vieques 

 (Crab Island); Icacos; Culebra (Snake 

 Island); Culebrita and some other 

 islets to the east. 



Porto Rico is reached by steamships 

 from New York in from three and one- 

 half to five days; St. Thomas and St. 

 Croix by steamers from New York in 

 five or six days, and there is regular 

 weekly interinsular steamship communi- 

 cation between Porto Rico, St. Thomas 

 and St. Croix. Excellent hotel and 

 boarding house accommodations are to 

 be had in all three of these islands. 

 The other islands of the archipelago are 

 reached only by motor-boats or sail 

 boats and accommodations for visitors 

 are meagre, and in order to study some 

 of them living on boats or camping is 

 necessary. N. L. B. 



II. PRESENT BIOTIC CONDITIONS 

 (N. L. B. AND G. N. W.) 



The littoral halophytic flora and 

 fauna of the province remains in its 

 pristine condition; it contains but few 

 species not found widely distributed on 

 the coasts of the other West Indies and 

 of continental tropical America. Ex- 

 cept locally, the original vegetation of 

 most of the area has been profoundly 

 modified, and many of the species have 

 become either very rare, or eliminated. 



Portions of the southwestern dry 

 districts are essentially in natural 



