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BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



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 afTccted. 



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- 

 ra])hy. This, as distinguished from the narrow strips of coastal plains 

 at its foot, which will be next described, ])rcsents 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. 



