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



Turning now to the submarine plateaus adjacent to Jamaica (Map^ 

 page 328), the soundings indicate the general character to be that of a 

 submerged table-land now 3,000 or 4,000 feet beneath the surface of 

 the sea. Across this submarine plateau, there are several deep trenches 

 like those of the Jamaican highlands but of greater magnitude, for 

 obvious reasons. Thus a few miles southwest of Jamaica, where the 

 edge of the shelf is covered by 4,800 feet of water, there is a drowned 

 channel 2,400 feet deeper. South-east of the island, before reaching 

 Morant Bay, another narrow valley is depressed to 5,000 feet, or 2,000 

 feet below the adjacent level of the plateau. The Kingston embay- 

 ment already shown in Figure 4, is another example. On approaching 

 Haiti, a characteristic embayment of great depth, surrounded by 

 steeply sloping sides, reaches to a depth of 4,000 feet below the floor of 

 the plateau, or 11,000 feet below the surface of the sea. Upon the 

 northern side of this same plateau, for a distance of over a hundred 

 miles, the drowned valley is conspicuous, having a breadth increasing to 

 twenty miles, and a depth of nearly 7,000 feet, with depressions 

 suggesting that it may generally reach to nearly 10,000 feet, while the 

 northern ridge is submerged only 4,000 feet. The head of this drowned 

 valley approaches the embayment near Haiti, and the trench connect- 

 ing them is considerably deeper than the general surface of the 

 submarine table-land. These deep channels dissecting the drowned 

 plateaus have very much the same ratio of their parts, but from two to 

 four times as great as the deep valleys of Jamaica, and they also receive 

 tributaries from various directions. The topographic forms suggest a 

 similar origin for the plateaus in the same general Mio-Pliocene period, 

 (whether above or below the surface of the sea), with the subsequent post- 

 Layton, that is to say, early Pleistocene, elevation of great proportion. 



A comparison of the erosion features before and after the Layton 

 epoch may admit of further explanation. The earlier erosion was 

 characterized by broad undulations (the period of the formation of the 

 plateau surface), proving the general degradation of the country, lasting 

 for a long period at base level of erosion, thus requiring a lower altitude 

 for the plateau on its great extension seawards. Probably both condi- 

 tions obtained, for a portion of the elevation of the interior district 

 appears due to a comparatively recent squeezing upward of the plateau 

 and mountain mass, as has been definitely observed in other islands. 

 Whether the terrestrial and submarine plateaus represent entirely 

 different steps of the Mio-Pliocene erosion features, or in part were once 

 a continuous base level, subsequently dislocated and modified, can 

 hardly be determined at present. Similar features are more perfectly 



