May 29, 1S84J 



NATURE 



"5 



ooze or a Pteropod ooze situated near continental shores and 

 deposits bearing the same names situated towards the centres of 

 oceanic areas, both with respect to mineral particles and remains 

 of organisms. 



Diatom Ooze. — This ooze is of a pale straw colour, and is com- 

 posed principally of the frustules of Diatoms. When dry it is a 

 dirty white siliceous flour, soft to the touch, taking the impres- 

 sion of the fingers, and contains gritty particles which can be 

 recognised by the touch. It contains on an average about 25 

 per cent, of carbonate of lime, which exists in the deposit in the 

 form of small Globigcrina shells, fragments of Echinoderms and 

 other organisms. '1 he residue is pale white and slightly plastic ; 

 minerals and fragments of rocks are in some cases abundant ; 

 these are volcanic, or, more frequently, fragments and minerals 

 coming from continental rocks and transported by glaciers. The 

 line washings consist essentially of particles of Diatoms along with 

 argillaceous and other amorphous matter. We estimate that the 

 frustules of Diatoms and skeletons of siliceous organisms make 

 up more than 50 per cent, of this deposit. 



Radiolarian Ooze. — It was stated, when describing a Globi- 

 gerina ooze, that Kadiolarians were seldom, if ever, completely 

 absent from marine deposits. In some regions they make up a 

 considerable portion of a Globigei ina ooze, and are also found in 

 Diatom ooze and in the terrigenous deposits of the deeper water 

 surrounding the land. In some regions of the Pacific, how- 

 ever, the skeletons of these organisms make up the principal 

 part of the deposits, and to these we have given the name " Radio- 

 larian ooze." The colour is reddish or deep brown, due to the 

 presence of the oxides of iron and manganese. The mine' at 

 particles consist of fragments of pumice, lapilli, and volcanic 

 minerals, rarely exceeding C07 mm. in diameter. There is not 

 a trace of carbonate of lime in the form of shells in some samples 

 of Kadiolarian ooze, but other specimens contain 20 per cent, 

 of carbonate of lime derived from the shells of pelagic Foramini- 

 fera. The clayey matter and mineral particles in this ooze are 

 the same as those found in the red clays, which we will now pro- 

 ceed to describe. 



Red Clay. — Of all the deep-sea deposits this is the one which 

 is distributed over the largest areas in the modern oceans. It 

 might be said that it exists everywhere in the abysmal regions of 

 the ocean basins, for the residue in the organic deposits which 

 has been described under the names Globigerina, Pteropod, 

 and Radiolarian ooze, is nothing else than the red clay. How- 

 ever, this deposit only appears in its characteristic form in those 

 areas where the terrigenous minerals and calcareous and sili- 

 ceous organisms disappear to a greater or less extent from the 

 bottom. It is in the central regions of the Pacific that we meet 

 with the typical examples. Like other marine deposits, this one 

 passes laterally, according to position and depth, into the adja- 

 cent kind 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 C05 mm. in dia- 

 meter. It is plastic and greasy to the touch ; when dried it 

 coagulates into lumps so coherent that considerable force must 

 be employed to break them. It gives the brilliant streak of clay, 

 and breaks down in water. The pyrognostic properties show 

 that we are not dealing with a pure clay, for it fuses easily before 

 the blowpipe into a magnetic bead. 



Under the term red clay are comprised those deposits in which 

 the characters of clay are not well pronounced, but which are 

 mainly composed of minute particles of pumice and other vol- 

 canic material which, owing to their relatively recent deposition, 

 have not undergone great alteration. If we calculate the analyses 

 of red clay, it will be seen, moreover, that the silicate of alumina 

 present as clay (2SiO, 2 , AU0 3 + 2ll.,0) comprises only a rela- 

 tively 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 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 accom- 

 panied by fragments of lapilli and of pumice more or less altered. 

 Vitreous volcanic matters belonging to the acid and basic series 

 of rocks predominate in the regions where the red clay has its 

 greatest development, and it will be seen presently that the most 

 characteristic decompositions which there take place are asso- 

 ciated with pyroxenic lavas. 



Associated with the red clay are almost always found concre- 

 tions and microscopic particles of the oxides of iron and man- 

 ganese, to which the deposit owes its colour. Again, in the 

 typical examples of the deposit, zeolites in the form of crystals 

 and crystalline spherules are present, along with metallic 

 globules and silicates which are regarded as of cosmic origin. 

 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 Foraminifera, 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, Radiolarians, and Sponge-spicules are 

 generally present, and are sometimes very abundant. The ear- 

 bones of various Cetaceans, as well as the remnants of other 

 Cetacean bones, and the teeth of sharks, are, in some of 

 the typical samples far removed from the continents, exceed- 

 ingly abundant, and are often deeply impregnated with, or 

 embedded in thick coatings of, oxides of iron and manganese. 

 The remains of these Vertebrates have seldom been dredged in 

 the organic oozes, and still more rarely in the terrigenous deposits. 

 The fine washings, as examined with a power of 450 diame- 

 ters, are composed of an amorphous matter, fragments of mine- 

 rals, the remains of siliceous organisms, and colouring substances. 

 What we call amorphous matter may be considered as properly 

 the argillaceous matter, and presents characters essentially vague. 

 It appears as a gelatinous substance, without definite contours, 

 generally colourless, perfectly isotropic, and forms the base 

 which agglutinates the other particles of the washings. As these 

 physical properties are very indefinite, it is difficult to estimate 

 even approximately the quantity present in a deposit. However, 

 it augments in proportion as the deposit becomes more clayey, 

 but we think that only a small quantity of this substance is neces- 

 sary to give a clayey character to a deposit. Irregular fragments 

 of minerals, small pieces of vitreous rocks, and remains of 

 siliceous organisms predominate in this fundamental base. These 

 particles probably make up about 50 per cent, of the whole mass 

 of the fine washings, and this large percentage of foreign sub- 

 stances must necessarily mask the character of the clayey matter 

 in which they are embedded. The mineral particles are seldom 

 larger than o'oi mm. in diameter, but descend from this size to 

 the merest points. It is impossible, on account of their minute- 

 ness, to say to what mineral species they belong : their optical 

 reactions are insensible, their outlines too irregular, and all 

 special coloration has disappeared. All that can be reasonably 

 said is that these minute mineral particles probably belong to the 

 same species as the larger particles in the same deposit, such 

 as feldspar, hornblende, magnetite, &c. In the case of pumice 

 and siliceous organisms the fragments can, owing to their struo- 

 ture, be recognised when of a much less size than in the case of 

 the above minerals. 



It can be made out by means of the microscope that the colour- 

 ing substances are hydrated oxides of iron and manganese. The 

 former is scattered through the mass in a state of very fine 

 division ; in some points, however, it is more localised, the 

 argillaceous matter here appearing with a browner tinge, but 

 these spots are noticed gradually to disappear in the surrounding 

 mass. The coloration given by the manganese is much more 

 distinct ; there arc small, rounded, brownish spots with a diame- 

 ter of less than o'oi mm., which disappear under the action of 

 hydrochloric acid with disengagement of chlorine. These small 

 round concretions, which are probably a mixture of the oxides 

 of iron and manganese, will be described with more detail in 

 the Challenger Report. 



The following table shows the nomenclature we have 

 adopted : — 



Shore formations, 



Blue mud, 



Green mud and sand 



Red mud, 



Terrigenous 

 deposits. 



Coral mud and sand, 

 Coralline mud and sand, 

 , Volcanic mud and sand, 



Found in inland 

 seas and along the 

 shores of con- 

 tinents. 

 Found about 

 oceanic islands and 

 along the shores of 

 continents. 



