DEEP-SEA FORMATIONS. 149 



is larger than the percentage of lime characteristic of true 

 chalk. 



On the western edge of the Florida Bank, northward of the 

 Tortugas, sponges occur in abundance, and the trawl would 

 constantly come up from a depth of one hundred fathoms 

 filled with masses of sponges, both siliceous and calcareous, 

 from a modern limestone bottom. Masses of fossil sponges 

 occur in the Jurassic beds of southern Germany and Switzer- 

 land, made up of calcified skeletons of Hexactinellidae and 

 of Lithistidse. Siliceous sponges are also common in the 

 ■white chalk of England and France. Calcareous sponges are 

 very abundant in some of the shallow- water beds of the creta- 

 ceous. 



Judging from my own experience, we must unquestionably 

 refer this supply of silica to the large fields of deep-sea siliceous 

 sponges, which when dead and decomposed supply the spicules 

 found scattered all through the calcareous mass of the deep-sea 

 globigerina ooze. These siliceous sponges are often found in 

 great numbers, as in the globigerina ooze off Santa Cruz for in- 

 stance, where numerous specimens of an interesting new Phe- 

 ronema were dredged, as many as ten to fifteen in a single haul. 

 The whole mass of the mud was so thoroughly impregnated with 

 spicules and with sponge sarcode as to be sticky and viscid. 

 More than once the dredge " must have plunged headlong into 

 one of the ubiquitous sponge-beds, — the glairy mass like white 

 of egg, with a multitude of spicules distributed like hair in 

 mortar throughout the mud." This, as well as the analyses of 

 the bottoms, plainly shows that the amorphous substance, giving 

 to the mud its viscidity, is not produced by sulphate of lime in 

 a flocculent state, but is due to the j^reseuce of a mass of decom- 

 posed protoplasm, — the remnants of all the animal life which 

 has accumulated for ages upon the bed of the ocean. This is 

 slowly used again by living animals, and kept from putrefac- 

 tion and decay, by being preserved, in the excess of carbonic 



mata contained over 98, and Porites only The remaining one to two per cent is 



95.8 per cent of carbonate of lime, made up of silica, magnesia, fluorine, 



These corals have about two per cent of phosphoric acid, and alumina and iron 



organic matter, which when fresh gives oxide, 

 a strong reaction for phosphoric acid. 



