NARRATIVE OF THE CRUISE. 
921 
the bottom. It is in the central regions of the Pacific that the typical examples are 
met with. Like other marine deposits, this one passes laterally, according to position 
and depth, into the adjacent kinds of deep-sea ooze or mud. 
The argillaceous matters are of a more or less deep brown tint from the presence of 
the oxides of iron and manganese. In the typical examples no mineralogical species can 
be distinguished by the naked eye, for the grains are exceedingly fine and of nearly 
uniform dimensions, rarely exceeding 0'05 mm. in diameter. It is plastic and greasy to 
the touch ; when dried it coagulates into lumps so coherent that considerable force must 
lie employed to break them. It gives the brilliant streak of clay, and breaks down in 
water. The pyrognostic properties show that it is not a jiure clay, for it fuses easily 
before the blow-pipe into a magnetic bead. 
Under the term red clay are comprised those deposits which do not conspicuously 
exhibit the characters of clay, but are mainly composed of minute particles of pumice 
and other volcanic materials that have not undergone great alteration owing to their 
relatively recent deposition. If the analyses of red clay be calculated, it will be seen, 
moreover, that the silicate of alumina present as clay (2Si0 2 ,Al 2 0 3 -1- 2H 2 0) comprises 
only a relatively small portion of the sediment ; the calculation shows always an excess of 
free silica, which is attributed chiefly to the presence of siliceous organisms. 
Microscopic examination shows that a red clay consists of argillaceous matter, minute 
mineral particles, and fragments of siliceous organisms ; in a word, it is in nearly all 
respects identical with the residue of the organic oozes. The mineral particles are for 
the greater part of volcanic origin, except in those cases where continental matters are 
transported by floating ice, or where the sand of deserts has been carried to great 
distances by winds. These volcanic minerals are the same constituent minerals of modern 
eruptive rocks, enumerated in the description of volcanic muds and sands ; in the great 
majority of cases they are accompanied by fragments of lapilli and of pumice more or less 
altered. Vitreous volcanic matters belonoing; to the acid and basic series of rocks 
predominate in the regions where the red clay has its greatest development, and the 
most characteristic decompositions which there take place are associated with pyroxenic 
lavas. 
Calcareous organisms are so generally absent in the red clay that they cannot be 
regarded as characteristic ; when present they are chiefly the shells of pelagic Foramini- 
fera, and are usually met with in greater numbers in the surface layers of the deposit, to 
which they give a lighter colour. On the other hand, the remains of Diatoms, Raclio- 
larians, and Sponge spicules are generally present, and are sometimes very abundant. 
The description of the fine washings of a Globigerina ooze (pp. 913, 914) applies in all 
respects to the finer parts of a typical red clay. The bones of Cetaceans, Sharks’ teeth, 
cosmic dust, manganese nodules, and zeolites, associated together in typical red clays, are 
referred to on p. 807. 
