166 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Cuba and extending eastward as far as Misteriosa Bank and into the 

 Gulf of Honduras. This valley reaches to Swan Island ; it is flanked un 

 the south by the gentler slope of the eastern end of Jamaica, and the 

 steeper lines of the western end of that island ; on the northern edge rise 

 the high mountains of the southern coast of Cuba, some of the peaks of 

 which attain a height of over eight thousand feet. This range is con- 

 tinued to the westward of Cape Cruz, and its summits are the Caymans 

 and the shoals of Misteriosa Bank. This valley is known as Bartlett's 

 Deep : it is in many places more than three thousand fathoms in depth. 

 The folds, islands, and banks which give the hydrography of the north- 

 ern, western, and eastern boundaries of the Caribbean so varied an ap- 

 pearance are in striking contrast to the great sea-sunken plains which 

 form the basin of the Caribbean and of the Gulf of Mexico. 



The steep slopes off the southern coast of Cuba due to the elevation 

 of that part of the island, as well as the slopes off the northern and south- 

 western shores of San Domingo, are fully as steep as any of the sea faces 

 of the Bahama banks. If in the one case, where the coral limestones 

 are of limited extent, we find no difficulty in interpreting the origin of 

 this slope, we should not in the other, where the reef limestones merely 

 form a capping to submarine folds which owe their origin to the same 

 causes, attempt to explain its existence in any other manner. 



THE BOTTOM AND ROCKS ON THE BAHAMA BANKS- 



The Bottom. 



The nature of the bottom a on the banks varies greatly according to the 

 locality. In proximity to the shores of the islands, where the sea is con- 

 stantly wearing away and disintegrating the seolian rocks, the bottom 

 consists of aeolian sand, varying in size according to the character of the 

 adjacent rocks from coarse composite grains to the finest, almost impal- 

 pable powder. As we pass into deeper water, 2 away from the influences 



1 Judging from the specimens of the bottom brought up in the dredge, the action 

 of the sea has still considerable force at a depth of nearly fifteen fathoms. 



2 By an unfortunate oversight, the coral ooze which extends only a comparatively 

 short distance from the 100 fathom line along the line of the Florida Reefs and of 

 the coast of Cuba is marked on the colored map of bottoms of the " Three Cruises of 

 the Blake" (Fig. 191) as extending all the way across the Straits of Florida. The 

 central part of the channel of the Gulf Stream should be colored to indicate the ex- 

 tension of the modified Pteropod and Globigerina ooze which covers so great a part of 



