June 5, 1884] 



NA TURE 



tion of the minerals and of the organic remains which are com- 

 monly associated with it. The origin of these vast deposits of 

 clay is a problem of the highest interest. It was at first sup- 

 posed that these sediments were composed of microscopic par- 

 ticles arising from the disintegration of the rocks by rivers and 

 by the waves on the coasts. It was believed that the matters held 

 in suspension were carried far and wide by currents, and gradu- 

 ally fell to the bottom of the sea. But the uniformity of com- 

 position presented by these deposits was a great objection to this 

 view. It could be shown, as we have mentioned above, that 

 mineral particles, even of the smallest dimensions, continually 

 set adrift upon disturbed waters must, owing to a property of 

 sea water, eventually be precipitated at no great distance from 

 land. It has also been supposed that these argillaceous deposits 

 owe their origin to the inorganic residue of the calcareous shells 

 which are dissolved away in deep water, but this view has no 

 foundation in fact. Everything seems to show that the forma- 

 tion of the clay is due to the decomposition of fragmentary vol- 

 canic products, whose presence can be detected over the whole 

 floor of the ocean. 



These volcanic materials are derived from floating pumice and 

 volcanic ashes ejected to great distances by terrestrial volcanoes, 

 and carried far by the winds. It is also known that beds of lava 

 and of tufa are laid down upon the bottom of the sea. This 

 assemblage of pyrogenic rocks, rich in aluminous silicates, de- 

 composes under the chemical action of the water, and gives rise, 

 in the same way as do terrestrial volcanic rocks, to argillaceous 

 matters, according to reactions which we can always observe on 

 the surface of the globe, and which are too well known to need 

 special mention here. 



The detailed microscopic examination of hundreds of sound- 

 ings has shown that we can always demonstrate in the argillaceous 

 matter the presence of pumice, of lapilli, of silicates, and other 

 volcanic minerals in various stages of decomposition. 



As we have shown in another paper, 1 the deposit most widely 

 distributed over the bed of modern seas is due to the decomposi- 

 tion of the products of the internal activity of the globe, and the 

 final result of the chemical action of sea water is seen in the 

 formation of this argillaceous matter, which is found everywhere 

 in deep-sea deposits, sometimes concealed by the abundance of 

 siliceous or calcareous organisms, sometimes appearing with its 

 own proper characteristics associated with mineral substances, 

 some of which allow us to appreciate the extreme slowness of its 

 formation, or whose presence corroborates the theory advanced 

 to explain its origin. 



In the places where this red clay attains its most typical deve- 

 lopment, we may follow, step by step, the transformation of the 

 volcanic fragments into argillaceous matter. It may be said to 

 be the direct product of the decomposition of the basic rocks, 

 represented by volcanic glasses, such as hyalomelan and tachy- 

 lite. This decomposition, in spite of the temperature approxi- 

 mating to zero (32° F. ), gives rise, as an ultimate product, to 

 clearly crystallised minerals, which may be considered the most 

 remarkable products of the chemical action of the sea upon the 

 volcanic matters undergoing decomposition. These microscopic 

 crystals are zeolites lying free in the deposit, and are met with 

 in greatest abundance in the typical red clay areas of the Central 

 Pacific. They are simple, twinned, or spheroidal groups, which 

 scarcely exceed half a millimetre in diameter. The crystallo- 

 graphic and chemical study of them shows that they must be 

 referred to Christianite. It is known how easily the zeolites 

 crystallise in the pores of eruptive rocks in process of decomposi- 

 tion ; and the crystals of Christianite, which we observe in 

 considerable quantities in the clay of the centre of the Pacific, 

 have been formed at the expense of the decomposing volcanic 

 matters spread out upon the bed of that ocean. 



In connection with this formation of zeolites, reference may 

 be made to a chemical process whose principal seat is the red 

 clay areas, and which gives rise to nodules of manganiferous iron. 

 This substance is almost universally distributed in oceanic sedi- 

 ments, yet it is not so much of the areas of its abundance that 

 we intend to speak as to the fact of its occurrence in the red clay. 

 because this association tends to show a common relation of 

 origin. It is exactly in those regions where there is an accumu- 

 lation of pyroxenic lavas in decomposition, containing silicates 

 with a base of manganese and iron, such for example as augite, 

 hornblende, olivine, magnetite, and basic glasses, that man- 

 ganese nodules occur in greatest numbers. In the regions where 

 the sedimentary action, : mechanical and organic, is, as it were, 



'Cn Cosmic and Vole; 



:Du:t," Proc. Key. Sec U,1n: 



suspended, and where, as will appear in the sequel, everything 

 shows an extreme slowness of deposition, — in these calm waters 

 favourable to chemical reactions, ferro-manganiferous.substances 

 form concretions around organic and inorganic centres. 



These concentrations of ferric and manganic oxides, mixed 

 with argillaceous materials whose form and dimensions are ex- 

 tremely variable, belong generally to the earthy variety or wad, 

 but pass sometimes, though rarely, into varieties of hydrated 

 oxide of manganese with distinct indications of radially fibrous 

 crystallisation. The interpretation to which we are led, in order 

 to explain this formation of manganese nodules, is the same as 

 that which is admitted in explanation of the formation of coatings 

 of this material on the surface of terrestrial rocks. These salts 

 of manganese and iron, dissolved in water by carbonic acid, then 

 precipitated in the form of carbonate of protoxide of iron and 

 r.ianganese, become oxidised, and give ■ ise in the calm and deep 

 oceanic regions to more or less pure fei o-manganiferous concre- 

 tions. At the same [time it must be admitted that rivers may 

 bring to the ocean a contribution of these same substances. 



Among the bodies which, in certain regions where red clay 

 predominates, serve as centres for these manganiferous nodules, 

 are the remains of Vertebrates. These remains are the hardest 

 parts of the skeleton — tympanic bones of whales, beaks of 

 Ziphius, teeth of sharks ; and just as the calcareous shells are 

 eliminated in the depths, so all the remains of the larger Verte- 

 brates are absent, except the most resistant portions. These 

 bones often serve as a centre for the manganese iron concretions, 

 being frequently surrounded by layers several centimetres in 

 thickness. In the same dredgings in the red clay areas some 

 sharks' teeth and Cetacean ear-bones, some of which belong 

 to extinct species, are surrounded with thick layers of the man- 

 ganese, and others with merely a slight coating. We will make 

 use of these facts to establish the conclusions which terminate 

 this paper. 



In these red clays there occur in addition the greatest num- 

 ber of cosmic metallic spherules, or chondres, the nature and 

 characters of which we have pointed out elsewhere. 1 We merely 

 indicate their presence here, as we will support our conclusions 

 by a reference to their distribution. 



Reviewing, then, the distribution of oceanic deposits, we may 

 summarise thus : — 



(1) The terrigenous deposits, the blue muds, green muds and 

 sands, red muds, volcanic muds and sands, coral muds and 

 sands, are met with in those regions of the ocean nearest to 

 land. With the exception of the volcanic muds and sands, and 

 coral muds and sands around oceanic islands, these deposits are 

 found only lying along the borders of continents and continental 

 islands, and in inclosed and partially inclosed seas. 



(2) The organic oozes and red clay are confined to the abysmal 

 regions of the ocean basins ; a Pteropod ooze is met with in 

 tropical and subtropical regions in depths less than 1500 fathoms, 

 a Globigerina ooze in the same regions between the depths of 

 500 and 2800 fathoms, a Radiolarian ooze in the central portions 

 of the Pacific at depths greater than 2500 fathoms, a Diatom 

 ooze in the Southern Ocean south of the latitude of 45° south, 

 a red clay anywhe-.e within the latitudes of 45 north and south 

 at depths greater than 2200 fathoms. 



Conclusions. — All the facts and details enumerated in the fore- 

 going pages point to certain conclusions which are of considerable 

 geological interest, and which appear to be warranted by the 

 present state of our investigations. 



We have said that the debris carried away from the land accu- 

 mulates at the bottom of the sea before reaching the abysmal 

 regions of the ocean. It is only in exceptional cases that the 

 finest terrigenous materials arc transported several hundred miles 

 from the shores. In place of layers formed of pebbles and clastic 

 elements with grains of considerable dimensions, which play so 

 large a part in the composition of emerged lands, the great areas 

 of the ocean basins are covered by the microscopic remains of 

 pelagic organisms, or by the deposits coming from the alteration 

 of volcanic products. The distinctive elements that appear in 

 the river and coast sediments are, properly speaking, wanting in 

 the great depths far distant from the coasts. To such a degree 

 is this the case that in a great number of soundings, from the 

 centre of the Pacific for example, we have not been able to distin- 

 guish mineral particles on which the mechanical action of water 

 had left its imprint, and quartz is so rare that it may be said to 

 be absent. It is sufficient to indicate these facts in order to 

 make apparent the profound differences which separate the de- 



• "On Cosmic and Volcanic Dust," Proc. Roy. Sor. Edin., 1883-84. 



