hill: geology of Jamaica. 23 



In general, all the Central Mountain structure occurs along three 

 lines of strike, probably representing the outcrop of two original lines of 

 corrugation, whose ends overlap en echelon. One is the Blue Mountain 

 liidge 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 the hills of 

 the back coast country, the mountain structure itself is found in the 

 bluffs on the north coast outcropping 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 area larger than the whole of the 

 present island, and, for reasons stated in our final chapter, related to 

 similar features of the other Great Antilles. 



The Plateau Region. — This later addition to the original island of 

 Jamaica is now a much dissected plain rising 3,000 feet. 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- 



FiGURB 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 



