274 



SKA 



amount of ferruginous matter* hiought down by 

 tin- rivers, anil it is then ral!e<l Ked Mini. Itlue 

 nm<l U estimated to cover aUmt 14,.VHl,000 sq. in. 

 of the earth's surface -I.IKKI.IKKI in the Arctic, 

 3.UOU.OOO in the I'uoilic, 2.50M.OOO in tlie Antarctic, 

 J.ii.im in tin- Atlaiiii.-. 1,300,000 in the Indian, 

 ami 1,600,OOU in the Southern Ocean. Ked iniul 

 covere alxmi IIHI.IHKI >.|. m. off the coast of Brazil. 



Ureen Mini ami Sand are similar to the blue 

 minis, but are characterised liy the presence of the 

 mineral glauconite in isolated grains or in small 

 concretions ; the dead shells of calcareous organ- 

 isms are usually tilled with the glauconite, which 

 gives the green colour to the deixwits. The sands 

 occur in the shallower water nearer the coast, and 

 in them the grains are larger than in the muds. 

 These deposits are found usually oil' high and bold 

 coast* where no very large rivers enter the sea ; for 

 instance, off the east coast of Australia, oil' South 

 Africa, ami oil' tin- west coast of North America, 

 (iri-eii mud and Hand cover about H.~>O, 000 sq. in. 

 300,000 in the Atlantic, 250,000 in the Pacific, 

 l.VI.OOO in the Indian, 90,000 in the Southern, and 

 60,000 in the Antarctic. 



Volcanic Mud and Sand are deposited around 

 the oceanic islands of volcanic origin, and the 

 name Is derived from the presence of fragments 

 and particle- of volcanic rocks and minerals, which 

 are larger and more numerous nearer the islands, 

 when tin- ilc|x>sit is called a sand, becoming smaller 

 and mixed with a larger percentage of pelagic 

 organic remains in the deeper water farther removed 

 from the coast, when the deposit is called a mud. 

 Volcanic mud and sand cover altout 600,000 sq. 

 m. 300,000 in the Pacific, 200,000 in the Atlantic, 

 and 100,000 in the Indian Ocean. 



Coral Mud and Sand occur similarly around the 

 oceanic coral islands and off those coasts and 

 islands fringed by coral-reefs, and are characterised 

 by the greater or less abundance of coral fragments 

 from the reefs. The sands are found in the 

 shallower water nearer the reefs, as in the case of 

 the volcanic sands. Coral mud and sand co\er 

 alMMit 2,557,000 sq. m. 1,417,000 in the Pacific, 

 760,000 in the Atlantic, and 380,000 in the Indian 

 Ocean. 



Of pelagic deposits there are five types, four of 

 organic origin, receiving their designations from 

 the distinctive presence of the remains of calcareous 

 or siliceous organisms, the fifth and most extensive 

 lieing of inorganic origin. 



(Jlobigerina Ooze is so called from the presence 

 of the dead shells of pelagic Foraminifera, those 

 lielongiiig to the genus (ilohigerina predominating. 

 which live in the surface and sub-surface waters of 

 the ocean, l>cing especially abundant in tropical 

 regions, and the shells of which after death fall to 

 the bottom and there accumulate in moderate 

 depths. The |>erccntage of carlionate of lime in the 

 deposit due to these shells and other calcareous 

 fragments varies from 30 to over 90, and there is 

 ii-ually nii admixture of minute mineral particles 

 and remains of siliceous organisms. The depth at 

 which <;ioliigcriim ooze is found varies from less 

 than fiOO to over 2.'X)0 fathoms, the average depth 

 being alMiut 2000 fathoms ; but there is a marked 

 difference lietween a sample collected in compara- 

 tively shallow water near land and one from deep 

 water toward- the central regions of the ocean 

 ba-ins. tin- point of union lieing the presence of a 

 considerable proportion of carUmate of lime shells, 

 (ilohigeriim ooze covers aliout 49,620,000 sn. in. 

 17,940,000 in the Atlantic, 11,300,000 in the Pacific, 

 10,360,000 in the Southern, and 9,720,000 in the 

 Indian Ocean. 



One of the facts brought ont by recent occano- 

 graphical researches is the gradual disappearance 

 of these calcareous shells from the de|Mwits of the 



deep sea with increasing depth in regions where 

 they may appear to be equally abundant at the 

 surface. In depths of over 3000 fathoms thi-e 

 shells are rare, and often there is not a trace of 

 carbonate of lime even in lesser depths, the (llobi 

 gerinu ooze being then replaced by one of the other 

 kinds ol jielagic deposit*. 



Pteropod Ooze resembles Globigerina ooze in all 

 respect-, except that there is a greater abundance 

 of the dead shells of pelagic Mollusca. such as 

 Pteropods ami llctcro|Kls ; it is usually found in 

 lesser depths than the ( Ilohigerina ooze. Pterojiod 

 ooze covers about 400,000 M|. m. in the Atlantic. 



The names applied to these oozes are not intended 

 to convey the idea that thev are wholly made up 

 of the organisms indicated by the names, or that 



these organisms form a preponderating propoiti 



for no deep sea deposit can lie said to DC strictly 

 homogeneous. Neither is there a sharp dividing 

 line between the various kinds of deposits; they 

 merge insensibly the one into the other. Often it 

 is difficult to locate a sample, one or other of the 

 names lieing equally applicable. 



Diatom Ooze is distinguished by the presence of 

 numerous remains of siliceous organisms, prin- 

 cipally Diatoms, though fragments of siliceous 

 Sponge spicules and Hadiolaria and Foraminifera 

 are rarely al>sent. It is found in the Antarctic 

 and Southern Oceans and also in the north-west 

 Pacific. Diatom ooze covers about 10,880,000 sq. 

 m. 10,000,0t;0 in the Southern, 840,000 in the 

 Antarctic, and 40,000 in the Pacific. 



Itadiolariiin Ooze in like manner contains a vary- 

 ing proportion of siliceous remains, in this case 

 principally liadiolaria and their fragment*. Cal- 

 careous organisms and mineral particles are nearly 

 always present in both these oozes, being usually 

 more numerous and the mineral particles larger in 

 the Diatom ooze than in the Kadiolarian oo/e, 

 which latter generally occurs in greater depth-. 

 than the former. The" Challenger's dee|)est sound- 

 ing, already mentioned, brought up a typical 

 Kadiolarian ooze, and it is found in the deeper 

 water of the central Pacific and Indian Oceans. 

 Kadiolarian ooze covers aliout 2,290,000 sq. m. 

 1,161,000 in the Pacific, and 1,129,000 in the Indian 

 Ocean. 



Ked Clay occupies nearly the whole of the deeper 

 abysses of the ocean, occurring in its most charac- 

 teristic form in the central regions of the Pacific, 

 for removed from continental land. It is of a 

 reddish or chocolate colour, due to the presence of 

 the oxides of manganese and iron. Fragments 

 of calcareous organisms are sometimes tolerably 

 abundant in the shallower depths, hut in a typical 

 red clay there is usually not more than a trace of 

 carbonate of lime. Siliceous remains are generally 

 present, and there is a small proportion of minute 

 mineral particles of volcanic origin, principally 

 derived from disintegrated pumice. Mineral par- 

 ticles of secondary origin, arising from the decom 

 [Kisition of volcanic debris, are associated with the 

 red clav, and in some regions of the central Pacific 

 isolated crystals and spheroidal groups of phillipsite 

 of secondary origin formed I'M mt<i make up a con- 

 siderable quantity of the deposit. Concretions of 

 manganese and iron are very characteristic of the 

 red clays, and may lie of all sizes, some! hues a large 

 <|uantiiy of the size of marbles, and sometimes the 

 size of potatoes, lieing procured. These concretions 

 are formed around various nuclei, such as sharks' 

 teeth, earlxmes of whales, ami pieces of pumice. 

 The Chttllenger sometimes procured over one 

 thousand sharks' teeth and sixty earbones of 

 whales in a single haul. The presence of the 

 remains of vertebrates, some of them belonging 

 to extinct sjiecies lying alongside others belong- 

 ing to existing species, as well as the formation ol 



