The Coastal Deserts of Jamaica. 131 



cennia nitida. The swamp merges into a series of saline flats 

 covered with Balis maritima and Poriulaca pilosa. Between the 

 flats and the desert hills and' stretching back between the flats 

 and the savannas is a zone of thorn forest made up almost ex- 

 clusively of a mesquite {Prosopis juliflora) known to Jamaicans 

 as the "cashew." This tree is very similar to the American 

 species of mesquite {Prosopis glandulosa and P. velutina) in habit 

 and the details of leaf and flower, and is probably similar in 

 possessing a deep root system enabling it to penetrate below the 

 layers of soil impregnated with salts by occasional tidal overflow 

 and to tap the underground seepage of fresh water from the 

 interior. i 



The entire south coast of Jamaica receives a light rainfall, 

 due to its being in the lee of the Blue ^Mountain range, which 

 reaches elevations of 4,000 to 7,400 feet directly in the path of 

 the prevailing north-east trade wind. Kingston, which lies in 

 the desert belt, receives 32 inches a year, and the large desert 

 areas to the west of Kingston undoubtedly receive much less. 

 This low rainfall is capable of supporting a savanna of coarse 

 grasses and large mimosaceous trees wherever the soil is deep, 

 as is true in the vicinity of Spanish Town, Porus and May Pen. 

 The desert, however, is sharply confined to limestone areas, 

 which have an extremely rough surface with thin layers or 

 shallow pockets of soil which are not capable of retaining mois- 

 ture nor of deriving it by capillarity. The close proximity of the 

 sea subjects these areas through the day to local sea breezes, and 

 during the early part of the night to land breezes — the con- 

 ditions being similar in fact to what they are in the small islands 

 of the Bahaman group where the trade wind blows constantly 

 but never discharges any of its moisture because of the low 

 elevation of the islands, resulting also in a high percentage of 

 sunshine. Soils similar to those of the Healthshire Hills which 

 are situated in the northern and central parishes of Jamaica, 

 where the rainfall reaches from 50 to 80 inches a year, support a 

 lofty and diversified forest. It requires, in other words, the 

 combined action of the low rainfall and the thinness of the soil 

 to favor the desert vegetation. 



The proximity of the sea and the existence of the sea breeze 

 not only makes the atmospheric humidity of the coastal deserts 



