326 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V. 



page 328). Physical maps show a mass of mountains intersected by 

 narrow valleys. This is true in a general way, yet structurally or 

 geomorphically, it is a plateau between 1,000 to 2,000 feet above the 

 sea. Some deep valleys almost cross the island and are reduced to 

 gentle gradients (Fig. i, Plate I.), even before leaving the mountain 

 masses. The margins of the table-lands are usually steep mountain 

 slopes dissected by deep valleys. In the interior, the elevated valleys 

 are often broad or form the savannas which appear to be the remains 

 of former base levels of erosion, not yet reduced to the modern plane of 

 denudation. The dissection of the margins of the higher land is pro- 

 gressing rapidly with the warm tropical rain which sometimes amounts 

 to ten inches a day,* and the gradients of the streams are such that the 

 widening of the valleys is no more rapid than the deepening of the 

 ravines. On the table-lands, many of the ridges are only the remains 

 of the former plains, but in the centre of the western two-thirds of the 

 island there are mountains 3,000 feet high. 



The eastern third of Jamaica is characterized by a mountain mass of 

 much higher altitude than the plateaus of the western two-thirds of the 

 island ; and it culminates in Blue Mountain which rises to 7,335 feet 

 above the sea. The rapid deepening of these valleys descending from 

 this high mass may be considered as gigantic washouts a thousand 

 feet deep ; and these are sometimes situated so close together that their 

 summit divides are scarcely more than knife edges (Fig. 2, Plate I.). 

 Still it is remarkable to observe the human occupation and cultivation 

 of sloping hillsides as steep as it is possible for the earth to hold to. 



In front of the coastal range of mountains on the northern side of the 

 island, which rise from 1,000 to 2,000 feet, the plains are almost 

 wanting, excepting at the mouths of the valleys (see Fig. i, Plate II., 

 page 335). On the southern side of Jamaica, the coastal plains may 

 have a breadth of four or eight miles in some embayments indenting the 

 plateau region (see Fig. 4, page 337). These plains may rise from 

 100 to 600 feet before abutting against the mountain ridges. 



In Jamaica there are the remains of three conspicuous old base planes 

 of denudation which give rise to the features of the island as shown in 

 Figure i. In some cases the lower plains approach the structure of 

 terraces, while those of the higher elevations are often only represented 

 by successions of ridges or remnants of eroded surfaces of the same 

 altitude. As the streams leave the highlands, they usually flow through 



*At Port Antonio situated upon the northern side of the Blue Mountain mass, which locally condenses the 

 moisture from the north-east trade winds, thirty-two inches of min fell within three days, in December, 1894. 



