140 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Deep-Sea Corals. He has called attention to the great width (compar- 

 atively speaking), varying from three to six miles, of the slope covered 

 by calcareous mud extending from the outer reef to the 100 fathom 

 line. This is in marked contrast with the narrow plateau found outside 

 of any reef on the Bahamas between it and the 100 fathom line. This 

 plateau is nearly always a mere narrow shelf, sometimes less than a 

 hundred feet, and rarely more than a mile in width at its greatest 

 breadth. 



An examination of the sections given on Plate IV. Figs. 1-3, and Plate 

 V. Fig. 16, will readily show the character of the slope of the bottom oft' 

 the Florida Keys, and the striking contrast of this slope with the steep, 

 almost vertical sides of the sea faces of the edges of the coral reef banks 

 of the Bahamas (Plate IV. Figs. 4, 5, 6, Plate V. Figs. 10, 15). Along 

 the Florida Reef, after passing the 100 fathom line, we find a rocky 

 belt of limestone built up of organic fragments of all kinds of Inverte- 

 brates, which extends very gradually to the 250 or 300 fathom line, 

 and has a greatest breadth of about eighteen miles off Sombrero Light. 

 Beyond this rocky belt, the Pourtales Plateau, the slope becomes 

 steeper towards the trough of the Gulf Stream. Off Cuba the rocky 

 slope is very abrupt (Plate V. Fig. 16), and this abrupt slope is char- 

 acteristic of the whole line of the Cuban coast, both north and south, 

 except along the face of the Old Bahama Channel. Figure 16 of 

 Plate V. is a section from Sand Key to Havana ; Figure 14 is a section 

 from Coffin's Patches to Elbow Cay on Salt Cay Bank. This shows with 

 great clearness the gentle slope off the reef to two hundred and thirty 

 fathoms, and the abrupt pitch of the Salt Cay Bank off Elbow Cay. 



The character of the sections across the trough of the Gulf Stream 

 becomes more clearly indicated in the sections from Fowey Eocks to 

 Gun Cay (Plate IV. Fig. 3), from Hillsboro Inlet towards the North- 

 west Providence Channel (Plate IV. Fig. 2), and from Jupiter Inlet to 

 Memory Rock (Plate IV. Fig. 1). The abrupt slope on the Bahama 

 Bank side characterizes all the sections. 



The sections of the two branches of the Old Bahama Channel passing 

 into the Straits of Florida on the two sides of Salt Cay Bank (Plate IV. 

 Fig. 5) show a more abrupt slope on the Cuban side than on the oppo- 

 site side off Salt Cay (Plate V. Figs. 13-15), where the slope is more 

 gentle ; while the section from Anguila to the opposite bank (Plate IV. 

 Fig. 6) shows its steepest slope off Anguila as compared with the 

 Bahama Bank slope. 



As we proceed eastward, the section from the Santa Maria Cays to the 



