May 



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NA TURE 



taken with a view of ascertaining the depth of the ocean, small 

 quantities of mud have been collected by the sounding lead and 

 briefly described. We may recall in this connection the experi- 

 ments of Ross and the observations of Hooker and Maury. 

 These investigations, made with more or less imperfect appli- 

 ances, immediately fixed the attention, without however giving 

 sufficient information on which to establish any general conclu- 

 sions as to the nature of the deposits or their distribution in the 

 depths of the sea. 



When systematic soundings were undertaken with a view 

 of establishing telegraphic communication between Europe 

 and America, the attention of many distinguished men was 

 directed to the importance, in a biological and geological sense, 

 of the specimens of mud brought up from great depths. The 

 observations of Wallich, Huxley, Agassiz, Baily, Pourtales, 

 Carpenter, Thomson, and many others, while not neglecting 

 mineralogical and chemical composition, deal with this only in a 

 subordinate manner. The small quantities of each specimen at 

 their command, and the limited areas from which they were 

 collected, did not permit the establishment of any general laws 

 as to their composition or geographical and bathymetrical distri- 

 bution. These early researches, however, directed attention to 

 the geological importance of deep-sea deposits, and prepared the 

 way for the expeditions organised with the special object of a 

 scientific exploration of the great ocean basins. 



The expedition of the Challenger takes the first rank in these 

 investigations. During that expedition a large amount of mate- 

 rial was collected and brought to England for fuller study under 

 the charge of Mr. Murray, who has in several preliminary papers 

 pointed out the composition and varieties of deposits which are 

 now forming over the floor of the great oceans. In order to 

 arrive at results as general as possible, it was resolved to investi- 

 gate the subject from the biological, mineralogical, and chemical 

 points of view, and M. Renard was associated with Mr. Murray 

 in the work. In addition to the valuable collections and obser- 

 vations made by the Challenger, we have had for examination 

 material collected by other British ships, such as the Porcufine, 

 Bulldog, Valorous, Nassau, Swallow, Dove ; and, through Prof. 

 Mohn, by the Norwegian North Atlantic Expedition. Again, 

 through the liberality of the United States Coast Survey and 

 Mr. A. Agassiz, the material amassed in the splendid series of 

 soundings taken by the American ships Tuscarora, Blake, and 

 Gettysburg, were placed in our hands. The results at which 

 we have arrived may therefore be said to have been derived from 

 a study of all the important available material. 



The work connected with the examination and description of 

 these large collections is not yet completed, but it is sufficiently 

 advanced to permit some general conclusions to be drawn which 

 appear to be of considerable importance. In addition to descrip- 

 tions and results, we shall briefly state the methods we have 

 adopted in the study. All the details of our research will be 

 given in the Report on the Deep- Sea Deposits in the Challenger 

 series, which will be accompanied by charts indicating the dis- 

 tribution, plates showing the principal types of deposits as seen 

 by the microscope, and numerous analyses giving the chemical 

 composition and its relation to the mineralogical composition. 

 The description of each sediment will be accompanied by an 

 enumeration of the organisms dredged with the sample, so as to 

 furnish all the biological and mineralogical information which 

 we possess on deep-sea deposits, and finally, we shall endeavour 

 to establish general conclusions which can only be indicated at 

 present. 



Before entering on the subject, we believe it right to point out 

 the difficulties which necessarily accompany such a research as 

 the one now under consideration, difficulties which arise often in 

 part from the small quantity of the substance at our disposal, but 

 also from the very nature of the deposit. Since we have endea- 

 voured to determine, with great exactitude, the composition of 

 the deposit at any given point, we have, whenever possible, 

 taken the sample collected in the sounding-tube. That procured 

 by the trawl or dredge, although usually much larger, is not 

 considered so satisfactory on account of the washing and 

 sorting to which the deposit has been subjected while being 

 hauled through a great depth of water. We have, how- 

 ever, always examined carefully the contents of these in- 

 struments, although we do not think the material gives such a 

 just idea of the deposit as the sample collected by the sounding- 

 tube. The material collected by the last-named instrument has 

 been taken as the basis of our investigations, although the 

 small quantity often gives to it an inherent difficulty. It was the 



small quantity of substance collected by the sounding-tube in 

 early expeditions which prevented the first observers from arriving 

 at any definite results ; but when such small samples are supple- 

 mented by occasional large hauls from the dredge or trawl, they 

 become much more valuable and indicative of the nature of the 

 deposit as a whole. Not only the scantiness of the material, but 

 the small size of the grains, which in most instances make up 

 deep-sea deposits, render the determinations difficult. In spile 

 of the improvements recently effected in the microscopical 

 examination of minerals, it is impossible to apply all the optical 

 resources of the instrument to the determination of the species 

 of extremely fine, loose, and fractured particles. Again, the 

 examination of these deposits is rendered difficult by the pre- 

 sence of a large quantity of amorphous mineral matter, and 

 of shells, skeletons, and minute particles of organic origin. It 

 is also to be observed that we have not to deal with pure and 

 unaltered mineral fragments, but with particles upon which the 

 chemical action of the sea has wrought great changes, and more 

 or less destroyed their distinctive characters. 



What still further complicates these researches is the endeavour 

 to discover the origin of the heterogeneous materials which make 

 up the deposits. These have been subjected to the influence of 

 a great number of agents of some of which our knowledge is to a 

 great extent still in its infancy. We must take into account a 

 large number of agents and processes, such as ocean currents ; 

 the distribution of temperature in the water at the surface and at 

 the bottom ; the distribution of organisms as dependent on tem- 

 perature and specific gravity of the water ; the influence of aerial 

 currents ; the carrying power of rivers ; the limit of transport by 

 waves ; the eruptions of aerial and submarine volcanoes ; the 

 effect of glaciers in transporting mineral particles, and, when 

 melting, influencing the specific gravity of the water, which in 

 turn affects the animal and plant life of the surface. It is neces- 

 sary to study the chemical reactions which take place in great 

 depths ; in short, to call to our aid all the assistance which the 

 physical and biological sciences can furnish. It will thus be 

 understood that the task, like all first attempts in a new field, is 

 one of exceptional difficulty, and demands continued effort to 

 carry it to a successful issue. 



In presenting a short resume of our methods, of the nomen- 

 clature we have adopted, and of the investigation into the origin 

 of the deposits in the deep sea and deeper parts of the littoral 

 zones, we offer it as a sketch of our research, prepared to modify 

 the arrangements in any way which an intelligent criticism may 

 suggest. 



Before proceeding to a description of methods and of the 

 varieties of deposits, with their distribution in modern oceans, 

 we will briefly enumerate the materials which our examination 

 has shown take part in the formation of these deposits, state the 

 origin of these materials, and the agents concerned in their depo- 

 sition, distribution, and modification. 



Materials. — The materials which unite to form the deposits 

 which we have to describe may be divided into two groups, 

 viewed in relation to their origin, viz., mineral and organic. 



The mineral particles carried into the ocean have a different 

 form and size, according to the agents which have been concerned 

 in their transport. Generally speaking, their size diminishes 

 with distance from the coast, but here we limit our remarks to 

 the mineralogical character of the particles. We find isolated 

 fragments of rocks and minerals coming from the crystalline and 

 schisto-crystalline series. i and from the clastic and sedimentary 

 formations ; according to the nature of the nearest coasts they 

 belong to granite, diorite, diabase, porphyry, &c. ; crystalline 

 schists, ancient limestones, and the sedimentary rocks of all geo- 

 logical ages, with the minerals which come from their disintegra- 

 lation, such as quartz, monoclinic and triclinic feldspars, horn- 

 blende, augite, rhombic pyroxene, olivine, muscovite, biotite, 

 titanic and magnetic iron, tourmaline, garnet, epidote, and other 

 secondary minerals. The trituration and decomposition of these 

 rocks and minerals give rise to materials more or less amorphous 

 and without distinctive characters, but the origin of which is 

 indicated by association with the rocks and minerals just 

 mentioned. 



Although the debris of continental land to which we have just 

 referred plays the most important rSle in the immediate vicinity 

 of shores, yet our researches show beyond doubt that when we 

 pass out towards the central parts of the great ocean basins, the 

 debris of continental rocks gradually disappears from the deposits, 

 and its place is taken by materials derived from modern volcanic 

 rocks, such as basalts, 'trachytes, augite-andesites, and vitreous 



