May 22, 1884] 



NA TURE 



87 



This is not the place to give the reasons which have guided us 

 in adopting this mode of description, or to give in detail the 

 methods that we have systematically employed for all the sedi- 

 ments which we are engaged in describing. These will be fully 

 given in the introduction to our Challenger Report. We limit 

 ourselves here to explaining the meanings and arrangement of 

 terms and abbreviations, so that the method may be understood 

 and made available for others. 



The description commences by indicating the kind of deposit 

 (red clay, blue mud, Globigerina ooze, &c), with the macrosco- 

 pic characters of the deposit, when wet or dry. 



We have always endeavoured to give a complete chemical 

 analysis of the deposit, but when it was impossible to do this we 

 have always determined the amount of Carbonate of Calcium. 

 This determination was generally made by estimating the car- 

 bonic acid. We usually took a gramme of a mean sample of 

 the substance for this purpose, using weak and -cold hydrochloric 

 acid. However, as the deposits often contain carbonates of 

 magnesia and iron as well, the results calculated by associating 

 the carbonic acid with the lime are not perfectly exact, but these 

 carbonates of magnesia and iron are almost always in very small 

 proportion, and the process is, we think, sufficiently accurate, 

 for, owing to the sorting of the elements which goes on during 

 collection and carriage, no two samples from the same station 

 give exactly the same percentage. The number which follows 

 the words " Carbonate of Calcium" indicates the percentage of 

 CaCO ;i ; we then give the general designations of the principal 

 calcareous organisms in the deposit. 



The part insoluble in the hydrochloric acid, after the deter- 

 mination of the carbonic acid, is designated in our descriptions 

 "Residue." The number placed after this word indicates its 

 percentage in the deposit ; then follow the colour and principal 

 physical properties. This residue is washed and submitted to 

 decantations, which separate the several constituents according 

 to their density; these form three groups — (1) Minerals, (2) 

 Siliceous Organisms, (3) Fine Washings. 



1. Minerals. — The number within brackets indicates the per- 

 centage of particular minerals and fragments of rocks. This 

 number is the result of an approximate evaluation, of which we 

 will give the basis in our report. As it is important to determine 

 the dimensions of the grains of minerals which constitute the 

 deposit, we give, after the contraction in. di., their mean diame- 

 ter in millimetres. We give next the form of the grains, if they 

 are rounded or angular, &c. ; then the enumeration of the species 

 of minerals and rocks. In this enumeration we have placed the 

 minerals in the order of the importance of the ro'e which they 

 play in the deposit. The specific determinations have been made 

 with the mineralogical microscope in parallel or convergent 

 polarised light. 



2. Siliceous Organisms. — The number between brackets indi- 

 cates the percentage of siliceous organic remains ; we obtain it 

 in the same manner as that placed after the word Minerals. The 

 siliceous organisms and their fragments are examined with the 

 microscope and determined. We have also placed under this 

 heading the glauconitic casts of the Foraminifera and other 

 calcareous organisms. 



3. Fine Washings. — We designate by this name the par- 

 ticles which, resting in suspension, pass with the first decanta- 

 tion. They are about 0*05 mm. or less in diameter. We have 

 been unable to arrange this microscopic matter under the cate- 

 gory of Minerals, for, owing to its minute and fragmentary 

 nature, it is impossible to determine the species. We have 

 always found that the Fine Washings increase in quantity as the 

 deposit passes to a clay, and it is from this point of view that the 

 subdivision has its raison d'Slre. We often designate the lightest 

 particles by the name argillaceous matter, but usually there are 

 associated with this very small particles of indeterminable 

 minerals and fragments of siliceous organisms. The number 

 within brackets which follows the words Fine Washings is ob- 

 tained in the same manner as those placed after Minerals and 

 Siliceous Organisms. 



These few words will suffice to render the descriptions intelli- 

 gible. Greater details will be given, as already stated, in the 

 Challenger Report. It may be added that in the majority of 

 cases we have solidified the sediments and formed them into thin 

 slides for microscopic examination, and that at all times the 

 examination by transmitted light has been carried on at the same 

 time as the examination by reflected light. Each description is 

 followed by notes upon the dredging or sounding, upon the 

 animals collected, and a discussion of the analysis whenever a 



complete analysis has been made, which is always the case with 

 typical samples of the deposits. 



Kinds of Deposits. — We now proceed to the description of the 

 various types of deposits into which it is proposed to divide the 

 marine formations that are now taking place in the deeper water 

 of the various oceans and seas. We will speak first of those 

 which are met with in the deeper water of inland seas, and 

 around the coasts of continents and islands, and afterwards of 

 those which are found in the abysmal regions of the great oceans. 

 Those coast formations which are being laid down on the shores, 

 or in very shallow water, and which have been somewhat care- 

 fully described previous to the recent deep-sea explorations, are 

 here neglected. 



A study of the collections made by the Challenger and other 

 expeditions show — 



(1) That in the deeper water around continents and islands 

 which are neither of volcanic nor coral origin, the sediments are 

 essentially composed of a mixture of sandy and am irphous 

 matter, with a few remains of surface organisms, to which we 

 give the name of muds, and which may be distinguished macro- 

 scopically by their colour. We distinguish them by the names, 

 blue, red, and green muds. 



(2) Around volcanic islands the deposits are chiefly composed 

 of mineral fragments derived from the decomposition of volcanic 

 rocks. These, according to the size of the grains, are called 

 volcanic muds or sands. 



(3) Near coral islands and along shores fringed by coral reefs, 

 the deposits are calcareous, derived chiefly from the disintegra- 

 tion of the neighbouring reefs, but they receive large additions 

 from shells and skeletons of pelagic organisms, as well as from 

 animals living at the bottom. These are named, according to 

 circumstances, coral or coralline muds and sands. 



Let us now see what are the chief characteristics of each of 

 these deposits. 



Blue mud is the most extensive deposit now forming around 

 the great continents and continental islands, and in all inclosed 

 or partially inclosed seas. It is characterised by a slaty colour 

 which passes in most cases into a thin layer of a reddish colour 

 at the upper surface. These deposits are coloured blue by 

 organic matter in a state of decomposition, and frequently give 

 off an odour of sulphuretted hydrogen. When dried, a blue mud 

 is grayish in colour, and rarely or never has the plasticity and 

 compactness of a true clay. It is finely granular, and occasion- 

 ally contains fragments of rocks 2 cm. in diameter ; generally, 

 however, the minerals, which are derived from the continents, 

 and are found mixed up with the muddy matter in these de- 

 posits, have a diameter of - S mm. and less. Quartz particles, 

 often rounded, play the principal part, next come mica, feldspar, 

 augite, hornblende, and all the mineral species which come from 

 the disintegration of the neighbouring lands, or the lands tra- 

 versed by rivers which enter the sea near the place where the 

 specimens have been collected. These minerals make up the 

 principal and characteristic portion of blue muds, sometimes 

 forming 80 per cent of the whole deposit. Glauconite, though 

 generally present, is never abundant in blue muds. The remains 

 of calcareous organisms are at times quite absent, but occasion- 

 ally they form over 50 per cent. The latter is the case when 

 the specimen is taken at a considerable distance from the coast 

 and at a moderate depth. These calcareous fragments consist 

 of bottom-living and pelagic Foraminifera, Mollusks, Polyzoa, 

 Serpulje, Echinoderms, Alcyonarian-spicules, Corals, &c. The 

 remains of Diatoms and Radiolarians are usually present. Gene- 

 rally speaking, as we approach the shore the pelagic organisms 

 disappear ; and on the contrary, as we proceed seawards, the 

 size of the mineral grains diminishes, and the remains of shore 

 and coast organisms give place to pelagic ones, till finally a blue 

 mud passes into a true deep-sea deposit. In those regions of 

 the ocean affected with floating ice, the colour of these deposits 

 becomes gray rather than blue at great distances from land, and 

 is further modified by the presence of a greater or less abundance 

 of glaciated blocks and fragments of quartz. 



(';,-■ n Muds and Sands.— As regards. their orgin, composition, 

 and distribution near the shores of continental land, these muds 

 and sands resemble the blue muds. They are largely composed 

 of argillaceous matter and mineral particles of the same size and 

 nature as in the blue muds. Their chief characteristic is the 

 presence of a considerable quantity of glauconitic grains, either 

 isolated or united into concretions. In the latter case the grains 

 are cemented together by a brown argillaceous matter, and in- 

 clude, besides quartz, feldspars, phosphate of lime, and other 



