Narrative of Bahama Expedition. 139 



dred<ring ground in the morning, (^ne of the most important 

 undertakings which our expedition had in view was a some- 

 what thorough exploration of the famous " Pourtales Plateau," 

 perhaps the richest tield in tiie WesLern Hemisphere for the 

 marine zoologist. Outside of the line of reefs known as the 

 Florida Reefs there extends southward a gentle submarine 

 slope reaching out toward the trough of the Gulf Stream. 

 '•This rocky plateau with a very moderate slope begins a 

 little to the westward of Sand Key, and stretches to the 

 northward and eastward until it reaches its maximum breadth, 

 of about eighteen miles to the eastward of Sombrero. It then 

 diminishes in breadth, and tinallv ends between Cary's Foot 

 Reef and Cape Florida. . . . The plateau begins at a 

 depth of about ninety fathoms, and ends at about three hund- 

 red.''^ The bottom is limestone composed of the debris from 

 the adjacent reefs, cemented into a sort of conglomerate. We 

 have here the most favorable condition for a profusion of ani- 

 mal life: — a gentle slope leading off from a continental mass, 

 for the real outline of the Florida Reefs include the whole line 

 of keys and reefs, bathed by a constant and powerful current. 

 Acting on the advice of Professor Alexander Agassiz, we 

 did all of our dredging on this plateau between Sand Key and 

 Sombrero Key. Taking our bearings from Sand Key Light, 

 American Shoal Light, and Sombrero Light; and frequenth' 

 getting cross-bearings from two of these, we were able to 

 know nearly our exact position during the w^hole time. With 

 some interruptions due to calms and a run into Key West for 

 a spar, we worked eleven days on the Pourtales Plateau, mak- 

 in£»; fortv-four hauls of the dred^"e or tangles. When the 

 weather permitted our dredging all day. we made six or 

 seven hauls daily. A comparison with our record while 

 dredging off Havana wall show that practice considerably 

 facilitated our work. We also found that the labor was much 

 less trying when we became used to it, although the heat was 

 considerably greater than we found it during our dredging off 

 the Cuban coast. Of course the comparative absence of sea- 



iThree Cruises of the Blake, \ol. I, p. 2S6. 



