SUBMARINE DEPOSITS. 289 



fragments of volcauic 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 jyer cent. This lime consisted of fragments of shells 

 of pelagic and other mollusks, of calcareous algae, of echinoderms, of an- 

 nelid tubes, of corals, polyzoa, alcyonarian spicules, coccoliths and rhab- 

 doliths, and of pelagic and other foraminifera. Where the shores were 

 composed of volcanic or other rocks not calcareous, the debris 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 volcanic muds light bi-own. 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 ci*ystalline grains of 

 carbonate of lime, but not the result of precipitation. A few sections 

 of globigerina and textnlaria were observed, but no other organisms 

 could be recognized. 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 which it was dredged, 



1 Monoclinie and triclinic feldspars, these deposits, and phosphatic grains 



hornblende, augite, olivine, magnetic iron, were like\vise rare. Altered fragments 



and pumice ; fragments from ancient of plagioclase, basalts, and diabase were 



rocks, as quartz, tourmaline, mica, epi- rather frequent, 

 dote. Glauconitic grrains were rare in 



