36 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
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 everywhere 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 débris 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 aro 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- 
tionalland 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 Vero, 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 River and Long Moun- 
tain through the parishes of St. Andrew and St, Catherine, to Claren- 
don Gully, some 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- 
