36 bulletin: museum of comparative zoology. 



The lowest reef constitutes a narrow rugose plain with a precipitous 

 undermining bluff at its seaward margin, as shown in Figure 13, and 

 occurs intermittently entirely around the island tipping the marginal 

 points as seen upon the geological map. The surface is weathered into 

 coarse, cavernous karrenfelder, the so called soborruco. 



The lowest marginal plain next to the sea to which this reef belongs 

 is a narrow strip of country seldom exceeding a half mile in width, and 

 occurs nearly everywliere between the water's edge and the back coast 

 bluffs. It is not everywhere composed of reef rock, however. In places it 

 is calcareous sand and marl, which in some instances represent old littoral 

 deposits and in others the debris which may have filled narrow lagoons 

 between the fringing reefs and the coast, and which have been synchro- 

 nously elevated with the reefs. 



Coast Plains of the Liguanea Type.- — The coastal plains and slopes 

 covered with alluvium are of a peculiar type, and represent old plains of 

 erosion ; they include ancient bights eroded out of the plateau margin, 

 and covered during long epochs of time by gravel and other aggrada- 

 tional land material. The deposits are composite in age, being contem- 

 poraneous in some stages of their history with the events of all three of 

 the terrace-making epochs. All plains of this character are not hori- 

 zontal, but have considerable slope from their interior margins towards 

 the sea, and at least, in the case of Liguanea, much of the aggradational 

 deposits were probably laid down as talus fans. These plains comprise 

 extensive areas indenting the back coast topography, especially on the 

 south side of the island, which is indented by them at eight places. In 

 the eastern portion the plains, like those at the mouth of the Plantain 

 Garden, the Negro, and the Yallahs Rivers, are more elongated and nar- 

 row than to the west, where as a rule they are much broader than they 

 are long. 



The most extensive of these phenomena is the Plain of Liguanea upon 

 which Kingston is situated (see Figure 8). This is over twenty-five 

 miles in length and averaging six miles in width. This is greatest near 

 its western end in the district of Vere, Parish of Clarendon, where it 

 is about fifteen miles. In all, it includes about 200 square miles. 

 In general, the plain has the outline of a parallelogram, extending 

 in an east and west direction from Hope I\iver and Long Moun- 

 tain through the parishes of St. Andrew and St. Catherine, to Claren- 

 don Gully, s<nne two miles west of Old Harbor. Its eastern and 

 western thirds border the coast, but its central third, south of Spanish 

 Town, is separated from the sea in two places; at one by the Port- 





