SEA-FLOOR DEPOSITS. PART I 299 



that some of these terms (presumably based on a necessarily casual examination on 

 board ship) are not sufficiently precise for a formal description. Moreover it is thought 

 desirable to modify the classification of Murray and Renard to a slight extent. 



It has long been recognized that the dividing line between pelagic and terrigenous 

 deposits is indefinite, and that deep-sea oozes may contain a slight proportion of 

 detrital material transported from areas of denudation. But many of the deposits named 

 "diatom ooze" in the official Station List have a predominance of detrital grains, 

 although diatoms may occur in considerable abundance. Here, such deposits are classi- 

 fied as " diatomaceous mud", a term which indicates the importance of both organic 

 and mineral material in their constitution. Some samples labelled "green mud" are 

 also placed in this new category. 



A constant feature of the diatomaceous muds is the abundance of flocculent material 

 which encloses and buoys up quantities of detrital mineral grains. This flocculent sub- 

 stance is apparently formed largely of perishable organic debris (such as algae and 

 animal plankton in various stages of decomposition), which is capable of drifting some 

 considerable distance. The flocculent masses must form an important factor in the 

 transport of terrigenous material which is sometimes found in surprising abundance at 

 considerable depth. As far as the writer is aware this factor has only been noted casually 

 in published works, but is evidently of wide application. The same phenomenon has 

 been observed in black muds (fetid with sulphuretted hydrogen and containing sporadic 

 oil globules) from the margins of the Wash, and from submerged banks in the estuary 

 of the River Mersey in England. Here, the organic debris clings round the detrital 

 quartz grains, and masses of the combined material float in moving water ; when move- 

 ment ceases they sink rapidly and soon become agglutinated. 1 The whole question seems 

 to call for detailed observation over a wider field. 



" Green mud ", as the term is usually defined, is distinguished by the abundance of the 

 mineral glauconite, which is sufficient to impart the characteristic green colour to the 

 deposit. In many of the so-called "green muds " in the Discovery collection, no grains 

 of glauconite have been noted. In these instances the green colour appears to be due to 

 the presence of chlorophyll, the green colouring matter which occurs in the chromato- 

 phores of diatoms and other algae, though often masked by other pigments. Much 

 organic debris occurs in such samples; in some the chlorophyll grains themselves are 

 visible, and in others the preservative liquid has become green by solution of the pig- 

 ment. It may be added that chlorophyll granules become brownish on decomposition 

 and oxidation, and thus may give rise to grey or brown muds. Hence mere colour is no 

 criterion of origin and should not be used as a guide to classification of the deposits. 

 Most of these "green muds" are more adequately described as diatomaceous muds. 

 The samples which do contain glauconite are here termed glauconitic muds in order to 

 indicate their characteristic quality more precisely. The quantity of glauconite is often 

 insufficient to impart a green colour to the sediment, but the presence of the mineral is 

 indicative of peculiar conditions in the sea water. 



1 Neaverson, E., 1928. Stratigraphical Palaeontology , p. 100, 8vo, London. 



