‘24 
THE VOYAGE OF H.M.S. CHALLENGER. 
ilescriptions, but, as already stated, the nature itself of the deep-sea deposits does not 
allow us to make a pnictical application of all the resources of microscopical analysis. 
Some other minenil particles composed of lapilli and fragments of rocks, manganese and 
iron concretions, phosphatic nodules, cosmic spherules, &c., will be described at length in 
the following chapters. 
3. Fine Washings. — It remains now to point out the characteristics of the third part 
of the residue, that denominated “ fine washings.” This portion comes away with the 
first decantations ; although in these decantations the substances composing the deposit 
are separated, as a rule, according to their specific gravity some particles of a higher 
density are always ciirried away with the lighter substances on account of their form 
and their very small size. Hence it may be expected that the fine washings obtained 
in this way will be a mixture of various substances in which predominate nevertheless 
the lightest and the smallest particles of the deposit. The somewhat vague term of 
fine washings appears to be preferable for this part of the residue to a mineralogical - 
name, such as clay, for instance. The fine washings are connected intimately with the 
two other groups of materials composing the residue — the siliceous organisms, and the 
mineral particles ; but the small size of these siliceous remains and of the fragments 
of minerals do not, as a rule, permit them to be classed with determinable species, and, 
on the other hand, in this part of the residue the amorphous matter predominates, 
forming, to the naked eye, a kind of homogeneous mass of a decidedly clayey character. 
Under the high powers of the microscope one observes that infinitesimal particles of 
organic and inorganic nature are imbedded in this argillaceous substance, which forms, 
so to 8})cak, the substratum of the whole. Hence in this heterogeneous aggregation, 
which comes under the name of fine washings, may be distinguished : — 
a. Argillaceous matter, forming small lumps with indefinite outlines, not reacting 
between crossed nicols, coloured or slightly tinted by other substances, reddish grey, 
browni.sh, &c., no gclatinisation with cold acids, after treatment with hydrochloric acid 
l>ecomes more or lc.ss colourle.ss, soluble after ebullition in sulphuric acid, heated on a 
platinum foil becomes red, yellowish, brownish, through the decomposition of the organic 
substances and dehydration and oxidation of the iron. Keaction of alumina with cobalt 
solution. The microstructure of this clayey matter is very indefinite, having, in wet 
[ircparations, a more or le.ss gelatinous a.spect in many instances. The colouring 
sub.stances arc niangancsc and iron, or one of them. The hydrated peroxide of 
manganc.-.Hc, in small microscojiic concretions or as a j)igment, is brownish, transparent, 
and di.s.HolvcH in strong hydrochloric acid setting chlorine free. With the manganese are 
gcncnilly associated, jis the colouring matter of the amorphous substances, oxides of 
iron, chieHy linnuiite, which arc dissolved in cold dilute hydrochloric acid. When this 
iron is not combined with the clay, it aj>pcars as small lamell®, as confused aggregations, 
giving to the clayey substance an ochreous or yellowish brown colour. With reflected 
