HILL: GEOLOGY OF JAMAICA. 23 
In general, all the Central Mountain structure occurs along three 
lines of strike, probably representing the outerop of two original lines of 
corrugation, whose ends overlap en échelon. One is the Blue Mountain 
Ridge proper; the others are represented by the buried summits of the 
west. The Blue Mountain Ridge is the most northern and eastern of 
these old corrugations, the Clarendon and Hanover exposures an inter- 
mediate one, and the Jerusalem the most southern and western. 
While the mountain eminences of the Central type nowhere extend to 
the immediate coast, and are everywhere separated from it by tho hills of 
the back coast country, the mountain structure itself is found in the 
bluffs on the north coast outeropping at the sea beneath the White 
Limestone Plateau. From this fact we conclude that, collectively, the 
Central Mountains of Jamaica represent an ancient mountainous topog- 
raphy, at one time occupying an atea larger than the whole of the 
present island, and, for reasons stated in our final chapter, related to 
Similar features of tho other Great Antilles. 
The Plateau Region. — This later addition to the original island of 
Jamaica is now a much dissected plain rising 3,000 feot. Its principal 
occurrence is west of the Blue Mountains, where it extends entirely 
across the island. In the east it constitutes a. narrow collar or dado of 
limestone country around the coastward margin of the Blue Mountain 
Ridge. In all, it occupies fully four fifths of the total area. 
As a whole, the profile of the plateau, could the irregularities of ero- 
Sion be eliminated, would be a very gentle arch, from whose east and 
west axis the surface slopes towards the adjacent seas. The curves of 
this arch if continued would not reach the sea at the present truncated 
margin of the land, but intercept it quite a distance beyond either shore, 
as shown in Figure 6, indicating that the former borders of the now re- 
P. 
ANS sea tevel " ai 
Fıaurn 6. Showing Truncated Margins and former Seaward Extension of 
Jamaica. — Dotted line shows Natural Profile. 
stricted island were extended. Thus in many places the margin of this 
plateau is marked by benches and terraces, constituting the back coast 
borders presently to be described. 
By tacit consent, the innumerable eminences of the plateau which rise 
to nearly 3,000 feet are called hills in Jamaica, to distinguish them from 
