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 Hexactinellide and 
of Lithistide. 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 viseidity, is not produced by sulphate of lime in 
a flocculent state, but is due to the presence 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 
organie matter, which when fresh gives oxide. 
a strong reaction for phosphoric acid. 
