HILL: GEOLOGY OF JAMAICA. 33 
belong to the lower group of levels. On the south coast the 650 feet 
level may be seen in the Yallahs topography, the summit of Round 
Mountain, at Vere, and the Healthshire Hills west of Port Royal en- 
trance, The 300 foot beach, or Bowden level, is very conspicuous around 
the east end of the island from Yallahs Mountain on the south to Port 
Antonio on the north, as well as on the west coast of the north side, at 
Cinnamon Hill and elsewhere in St. Ann, Trelawney, and St. James. 
The back coast benches enumerated have all been cut out of the land 
by gradational processes (base levelling and marine erosion) and represent 
Pausation stages in two long continued periods of elevation. Those be- 
tween 700 and 2,000 feet were carved out of the white limestone matrix 
during the first period of emergence from the sen. The benches, from 
100 to 700 feet in altitude are also cut out of the old limestone matrix, 
but were probably made during a second period of emergence and erosion 
following a period of subsidence as is explained later on. 
This abrupt ending of the land, considered in connection with its ac- 
Companying terraces, the arch of the summit region, and the narrow 
submerged platform around the island, strongly suggests, as outlined in 
the geologic chapters of this paper, that the Limestone Plateau was once 
More extensive land, which, after its first elevation, underwent marginal 
erosion, drowning of its coastal plains by partial subsidence, and re-ele- 
vation into its present outline. 
From the data given in the geologic portion of this paper, the time of 
these events was between the beginning of the Miocene (late Oligocene) 
and Pliocene time. There is much evidence that old gradational terraces 
of this type continue lower down upon the submerged slopes of the 
island, and that the phenomena of the Coastal Plain, next to'be described, 
represent veneerings of organic, littoral, and terrigenous deposits upon 
old erosion planes of this character, 
Benches of the Coast Plains, — A narrow strip of low land extends 
More or less interruptedly around the island, between the sea and the 
back coast border. In some places this is an old beach only a few feet 
Wide; in others it has greater width and indents the back coast border 
for miles. This coastal strip is composite in character, being of three 
types of formations, such as elevated reef rock, marginal sea débris, and 
land derived alluvium. It presents distinct features of relief, including 
Several benches of different height and origin, and a long and gentle 
Slope known as tho Liguanea Plain. The basements of these benches 
are old erosion levels which were submerged, covered with a veneering 
of constructional material, and re-elevated into land. 
VOL. XXXIV. 8 
