NARRATIVE OF THE CRUISE. 
919 
volcanic minerals, but oft’ barrier and fringing reefs facing continents there may be a great 
variety of rocks and minerals. Beyond a depth of 1000 fathoms oft’ coral islands the 
debris of the reefs begins to diminish, and the remains of pelagic organisms to increase ; 
the deposit becomes more argillaceous, of a reddish or rose colour, and gradually passes into 
a Globigerina ooze or a red clay. Coral sands contain much less amorphous matter than 
coral muds, but in other respects they are similar, the sands being usually found nearer 
the reefs and in shallower water than the muds, except inside lagoons. In some regions 
the remains of calcareous algse predominate, and in these cases the name coralline mud 
or sand is employed to point out the distinction. These deposits have a much greater 
resemblance to the White Chalk than has a Globigerina ooze. 
Beyond an average distance of about 200 miles from land, the deposits are characterised 
by the great abundance of fragmentary volcanic materials which have usually undergone 
great alteration, and by the enormous abundance of the shells and skeletons of minute 
pelagic organisms which have fallen to the bottom from the surface waters. These true 
deep-sea or abysmal deposits may be divided into those in which the organic elements 
predominate, and those in which the mineral constituents play the chief part. 
Globigerina Ooze. — Thus are designated all those truly pelagic deposits containing over 
40 per cent, of carbonate of lime, which consists principally of the dead shells of pelagic 
Foraminifera — Globigerina, Orbulina, Pulvimdina, Pullenia, Sphceroidina, &c. ; in the 
tropics some of the Foraminifera shells are visible to the naked eye. In some localities this 
deposit contains 95 per cent, of carbonate of lime. The colour is milky white, yellow, 
brown, or rose, these variations depending principally on the relative abundance in the 
deposit of the oxides of iron and manganese. This ooze is fine grained ; when dried 
it is pulverulent. Analysis shows that the sediment contains, in addition to carbonate of 
lime, phosphate and sulphate of lime, carbonate of magnesia, oxides of iron and manganese, 
and argillaceous matters. The residue is of a reddish brown tinge. Lapilli, pumice, and 
glassy fragments, often altered into palagonite, seem always to be present, and are 
frequently very abundant. The mineral particles are generally angular, and rarely 
exceed 0’08 mm. in diameter ; monoclinic and triclinic felspars, augite, olivine, hornblende, 
and magnetite are the most frequent. When quartz is present, it is in the form of 
minute, rounded, probably wind-borne grains, often partially covered with oxide of iron. 
More rarely white and black mica, bronzite, actinolite, chromite, glauconite, and 
cosmic dust are found. Siliceous organisms are probably never absent, sometimes 
forming 20 per cent, of the deposit, at other times they are only recognisable after 
careful microscopic examination. In some regions the frustules of Diatoms predominate, 
in others the skeletons of Radiolarians. 
Pteropod Ooze. — This deposit differs in no way from a Globigerina ooze except in the 
presence of a greater number and variety of pelagic organisms, and especially in the 
presence of Pteropod and Fleteropod shells, such as Diacria, Atlanta, Styliola, Carinaria. 
(narr. chall. exp. — vol. i. — 1885.) 116 
