30 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
found narrow outlets through single gorges. Still others, like the basin 
of Westmoreland, have had their coastward barriers largely destroyed. 
In all, they are interesting features of the decay of the limestone 
plateau. The entire series of depressions we have described — the first 
incipient “ hog-wallow "-like swales of the plateau, the acute cockpits, 
the small well shaped sinks of the Hampshire type, the great expanded 
basins of St. Thomas and Clarendon, and the old basins which have 
had their barriers partially broken away —are a series of connected 
phenomena, and illustrate the powerful effect of solution and erosion 
in producing the hilly topography of the White Limestone districts of 
Jamaica and the Tropics in general, and in degrading the plateau to the 
level of the sea, Should the island undergo no more uplift, the agency 
Figure 8. View of Back Coast Border from Rock Fort. 
of solution alone would ultimately entirely remove the white limestones 
now veneering the older foundation of insoluble Blue Mountain rocks 
underlying them. Not only has the plateau region undergone vertical 
disintegration by erosion and solution, but, as will now be shown, its 
margins have been similarly affected. 
Topography of the Back Coast Border. — The former areal extent 
of Jamaica has been constricted by the horizontal planing away of its 
seaward margin, as shown by a further study of the back coast topog- 
raphy. This, as distinguished from the narrow strips of coastal plains 
at its foot, which will be next described, presents a steeply sloping 
mountainous sea front rising sharply above the sea except where cut 
through by transecting drainage, and its skyline has an average altitude 
of 1,200 feet along the north coast. 
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