1897-98]- LATE FORMATIONS AND GREAT CHANGES OF LEVEL IN JAMAICA. 329 



tion the Wag Water, perhaps the largest river of the island, discharges, 

 and during floods it carries great quantities of silt, yet the bay is not 

 filled up, and at only a mile from its head, the channel is 624 feet deep. 

 Dry Harbour is another kind of basin, only a mile across (and sur- 

 rounded by an amphitheatre of hills), having a depth of 204 feet with 

 the outlet now obstructed by a bar covered with less than 18 feet of 

 water. These short, deep bays are like the valleys forming the amphi- 

 theatre indenting the margins of the table-lands of Mexico and other 

 plateau regions (also illustrated in Fig. 2, Plate II., opposite page 335). 



The broad shelf upon the southern side of Jamaica is only a continua- 

 tion of the sloping coastal plains. It has a breadth reaching eight or 

 ten miles from the shore, and it is covered with from a few to nearly a 

 hundred feet of water. This submerged plateau appears to have 

 extended from the end of the Blue Mountain chain, in St. Davids, 

 across the Kingston embayment and thence to the mountains bej'ond 

 Savanna la Mar. However, the two ends of the submarine shelf have 

 almost disappeared, but there are outlying remains of it preserved in 

 the banks or shoals. Thus the water, at less than a mile from the shore 

 in the Kingston embayment, is over 600 feet deep, and at three miles 

 2,300 feet, but increasing so that at ten miles, opposite to the California 

 bank, the depth of water is 4,662 feet (see Map, page 328, and Fig. 4, 

 page 337). The Savanna la Mar embayment, at the western end of 

 the shelf, had a depth of 1,974 ^'^^t near the shore, and 2,010 at the 

 mouth opposite to the bank eight miles distant. Both of these embay- 

 ments are submerged reproductions of the broader valleys, indenting 

 the table-land of the southern side of the island, which are covered with 

 the later alluvial deposits. 



Across the shallow banks the channels of the rivers can be traced. 



Unlike the Honduras sea, upon the northern side of Jamaica, which 

 rapidly descends to abysmal depths, the Caribbean sea to the south 

 deepens gradually for many leagues ; consequently there are no 

 drowned valleys near the insular mass deeper than 5,000 feet. Ex- 

 tending south-westward from Jamaica, there is a broad plateau reaching 

 to the Pedro bank which is cov^ered with from 3,000 to 4,000 feet of 

 water. From the north-western side of this plateau there is a deep 

 channel of 7,128 feet, or 2,400 feet below the platform, beyond which 

 the Honduras sea reaches to abysmal depths (see Map, Fig. 2, page 

 328), of 15,000 feet. Pedro bank is again connected with the banks 

 extending to the Honduras coast by a broad plateau now drowned 

 beneath 3,000 feet of water. 



