128 Part II. Chapter 1. 
The materials of the marginal table-land are soluble limestones which 
were formed as calcareous oceanic sediments. The configuration of the hilly 
country in the western side of the island owes its character largely to the 
solution of the limestone rock. The summit surface of the plateau is a hilly 
country filled with sink-holes, or cockpits, which represent deep basin-shaped 
valleys with deep drainage to the sea. The cockpit country, which has never 
been crossed, owes its topography to these cockpits, which are separated from 
each other by rounded conical hills rising above them. The seaward margin 
of the plateau, according to HILL‘), presents a sloping mountainous front rising 
to an average altitude of 1200 feet along the north coast. At Montego Bay, 
it is finely shown in a series of six benches which rise above the sea. The 
highest of the old benches is John Crow ridge (circa 2100 feet) separated from 
the Blue Mountains by the deep gorge of the Rio Grande. The next level’ 
(1500 feet) is seen in Long Mountain east of Kingston. A third step has an 
altitude of about 1000 feet and is found on the north side of the island, as 
a great dissected plain. A lower group of levels are found at 650, 300 and 
200 feet, respectively, which have been cut out of the old limestone matrix 
during a later period of emergence followed by a subsidence. 
The lowland of the coast consists of three types of formations, such as 
elevated reefs, marginal sea debris and alluvial deposits. Liguanea Plain is 
one of the most important topographic low land features. It is over 25 miles 
long by 6 miles wide and has an area of 200 square miles (518 qkm). 
This plain is comparatively bare and sterile, presenting in its xerophytic flora 
a striking contrast to the flora of the rest of the island. Such a plain, as 
Liguanea, is a record of four distinct events according to HILL: (1) the original 
cutting out of the matrix during a period of base leveling: (2) the filling in of 
the material constituting the present surface; (3) the elevation of the plans 
into their present position above the sea; and (4) the cutting of the modern 
streamways across them. x 
Jamaica abounds in streams of which two hundred have been described. 3 
The Rio Cobre drains the beautiful valley of St. Thomas-in-the-Vale by ten 
afduents which unite in a single trunk stream to flow through the Bog Walk 
Canyon. Wag Water River drains the northern slopes of the Blue Mountain 
range. Montego River, Great River and Black River drain the marginal slopes 
of the Cockpit country. The Minho River is an important stream draining 
into the Caribbean Sea near Portland Point. Salt River and the Cabaritta OR 
the south side are navigable to barges, while many of the streams are roaring 
and turbulent in their flow from the highlands of the interior. 
In geological conclusion the Blue Mountain series of rocks are of Eocene 
and Upper Cretaceous age. The older white oceanic limestones are perhaps$ 
KA - 
ı) Hırr, Roserr T.: A Sketch of the Geology of Jamaica. The Seottish Geograpbieal 
Magazine XV: 631. December 1893; Bulletin of the Museum of Comparative Zoology Har 
College XXXIV. Rn 
