62 THREE CRUISES OF THE " BLAKE." 



of this folding, the formation of an immense submarine plateau, 

 directly in the track of the Gulf Stream, by the accretions of 

 the solid parts of mollusks, echinoderms, corals, halcyonoids, 

 annelids, Crustacea, and the like, which have lived and died 

 upon it ; these solid parts have furnished the limestone for the 

 gradual completion of the peninsula. No one who has not 

 dredged near the hundred-fathom line on the west coast of 

 the great Florida plateau can form any idea of the amount of 

 animal life which can be sustained upon a small area under 

 suitable conditions of existence. It was no uncommon thing 

 for us to bring up in the trawl or dredge large fragments of 

 the modern limestone now in process of formation, consisting 

 of the dead carcasses of the very species now living on the 

 top of this recent limestone. To the westward of the western 

 shore line, Florida now stretches out as an unmense submarine 

 plateau, forming, as the sections show, a huge tongue coated or 

 veneered only by coral limestone over its very top. The whole 

 of the peninsula of Florida south of St. Augustine, as far as 

 Tampa Bay, has probably in this way been built up from north 

 to south, of limestone somewhat older than the reef limestone. 

 The plateau, judging from the inclination of the axis, has but a 

 slight southward dip until one reaches the southern extremity of 

 the peninsula, where the fall is more rapid toward the outer reef. 

 The whole of the eastern and western edges of Florida con- 

 sist of recent limestones, the immediate predecessors of that 

 which is now forming on the western and southern slopes of 

 the great Florida plateau. The early dredgings of Mr. Pour- 

 tales, in 1867 and 1868, developed on the Gulf Stream slope 

 off the Florida reefs an extensive rocky plateau (Pourtales 

 Plateau) from a depth of about ninety fathoms to about two 

 hundred and fifty fathoms. The rock of which this plateau is 

 built (see Fig. 192) consists of the same species of corals and 

 shells as those now living upon it, to which it owes its forma- 

 tion.^ A similar sea-bottom is found on the north side of Cuba, 



^ Mr. S. P. Sharpies, who examined of lime, the balance being organic matter 



specimens of rock from the Pourtales and phosphate of lime. 

 Plateau, found the corals made up of The recent limestone found on the 



about ninety-five per cent, of carbonate Pourtales Plateau contained from thirty- 



