SUBMARINE DEPOSITS. 289 
fragments of volcanic rocks, or crystals derived from these) In the 
deposits farthest from land the size of the mineral particles seldom 
exceeded 0.1 mm. in diameter, but near shore they were very much 
larger, and fragments of rocks and pebbles were frequently dredged. 
“The percentage of carbonate of lime in these deposits was usually 
very high, being frequently seventy or eighty per cent, and in the case 
of a chalk rock 90.24 per cent. · This lime consisted of fragments of shells 
of pelagic and other mollusks, of calcareous algæ, of echinoderms, of an- 
nelid tubes, of corals, polyzoa, aleyonarian spicules, coccoliths and rhab- 
doliths, and of pelagic and other foraminifera. Where the shores were 
composed of volcanic or other rocks not calcareous, the débris of these 
made up the larger part of the deposits, which might be called volcanic 
muds. But the majority of the deposits should be termed pteropod or 
globigerina ooze, owing to the large number of these organisms present 
in them. The ooze varies greatly in color. The pteropod ooze is either 
a white, a yellowish brown, or a dark brown; the globigerina ooze 
ranges from a light gray to light brown, the coral muds are yellowish 
and white, and the voleanie muds light brown. The darker-colored 
ooze and mud usually occur nearer shore than the lighter ooze found in 
the central parts of the basin of the Gulf of Mexico and in the Carib- 
bean. It should be remembered, however, that, both in the size of the 
mineral particles and the nature of a large number of the calcareous 
particles, these deposits differ considerably from similar deposits found 
far away from land in the open ocean, and called also pteropod and glo- 
bigerina ooze. 
* The siliceous organisms never make up more than four or five per 
cent of the whole deposit, and consist of radiolaria, sponge spicules, and 
a few diatoms. 
« From 994 fathoms, off Nuevitas, Cuba, there was obtained a frag- 
ment of white chalk coated on the surface with streaks of peroxide of 
manganese. This chalk contained 90.24 per cent of carbonate of lime. 
The sections showed the rock to be composed of crystalline grains of 
carbonate of lime, but not the result of precipitation. A. few sections 
of globigerina and textularia were observed, but no other organisms 
could be reeognized. After dissolving away a considerable quantity, 
small fragments of quartz and hornblende, sponge spicules, and radi- 
olarians were recognized in the residue. It is not possible to be certain 
that this rock was formed in the position from whieh it was dredged, 
1 Monoclinic and triclinie feldspars, these deposits, and phosphatie grains 
hornblende, augite, olivine, magnetic iron, were likewise rare. Altered fragments 
and pumice; fragments from ancient of plagioclase, basalts, and diabase were 
rocks, as quartz, tourmaline, mica, epi- rather frequent. 
dote. Glaueonitie grains were rare in 
