162 bulletin: museum of comparative zoology. 



north side. The platforms were covered with littoral formations and 

 the estuaries filled with aggradational debris. This submerged the 

 island to the foot of the back coast country. It clearly took place 

 during the late Pliocene and beginning of Pleistocene time. 



The next and last event was the epeirogenic elevation, or series of 

 elevations, which have continued until the present time, restoring to 

 the island the belt of land now forming the fringing coastal border, 

 including the elevated reefs. 



The continuity of this uplift- may have been interrupted by a minor 

 subsidence in early Pleistocene time. Unfortunately paleontologists have 

 not sufficiently analyzed the West Indian marine faunas to enable us to 

 discriminate between the Pliocene, Pleistocene, and recent faunas, espe- 

 cially the last. Hence the differentiation of the stages of Post-Pliocene 

 chronology is still vague. As the pre-submerged platforms of the preced- 

 ing epoch of subsidence were brought up within the zone of reef coral 

 growth, the first true coral reefs began to fringe the island and formed 

 outlying and fringing reefs. As elevation progressed, the oldest of these 

 were first raised above the sea into a bench of Soboruco, while new 

 living reefs were installed upon that portion of the submerged platform 

 which the elevation in turn brought up to a position favorable for reef 

 growth. Thus successive reefs were elevated into coastal benches, while 

 living reefs continued to grow in the adjacent waters, as are found to- 

 day! In this manner, as the island was constantly rising, the terraces 

 of reef rock now found at altitudes of 60, 25, and 15 feet, as described 

 in the geologic portion of this paper, were made. Similar living reefs 

 continued to grow as now in the adjacent waters, which in turn may 

 some day be elevated into marginal terraces. Inasmuch as the elevated 

 reefs arc made up entirely of living species, there is no reason to assign 

 this elevation to a more remote period than late Pleistocene and recent 

 time. 



Accompanying their elevation the lagoonal debris behind the barrier 

 reefs was also converted into low coastal swampy lands, and the streams 

 renewed their channels to the sea across the old alluvial plains. This 

 elevation completed the geographic evolution of Jamaica into the land 

 area it presents to-day. 



From the foregoing statements it will be seen that the evolution of 

 Jamaica has resulted from varied processes of land construction, includ- 

 ing, first, piling up of volcanic cjecta in the beginning of its history, 

 which we shall not further mention at present ; and two kinds of up- 

 lifts, erogenic and epeirogenic movements respectively. 



