April 1, 1893.] 



KNOWLEDGE. 



65 



DEEP SEA DEPOSITS. 



By Key. H. N. Hutchinson, B.A., F.G.S., Antlior nf 



" Extinct Monsters.'' 



[Second Paper.] 



HAVING, in our previous paper, given a general 

 idea of the classification and geographical dis- 

 tribution of deep sea deposits, we now pass on 

 to consider the diiierent kinds somewhat in 

 detail. In the scheme given on page 45 it was 

 shown that, classifying them by their composition, they 

 may be arranged in two groups, (1) Pelagic, (2) Terrige- 

 nous. Those of the first group are all organically-formed 

 oozes, except one, the red clay ; and may therefore rightly 

 be called pelagic, since they are all born of the sea. Those 

 of the second group are derived from land, or in other 

 words, are products of denudation ; hence the term " ter- 

 rigenous " (earthborn). We will begin with the pelagic 

 deposits. These are generally to be foimd in situations 

 far from land, and one of them (the red clay) always in 

 the deepest hollows of the ocean bed. Their characteristic 

 mineral particles either have a volcanic origin, or are of 

 secondary origin, i.e., have been formed by some of the 

 wonderful and little known chemical actions taking place 

 on the tloor of the deep ocean. Classifications are useful 

 in their way, but are sometimes apt to be misleading, and 

 the reader must be warned against supposing that no land- 

 derived material ever finds its way into a pelagic deposit, 

 or (•/(■(' i-trsd, that no pelagic organisms (such as make up 

 most of the oozes) ever enter into the composition of the 

 terrigenous deposits. It is really a question of percentages ; 

 and just as a town where the majority vote Liberal may be 

 called a "Liberal " constituency, so a deposit of which the 

 majority (or even a fair percentage) of its myriad individual 

 units or particles are of pelagic origin may be called 

 " pelagic." It is important to bear this in mmd, otherwise 

 the scheme of classification alluded to will convey a wrong 

 idea. With the exception of the red clay, all the pelagic 

 deposits are organic cozes princiiniUi/ composed of the 

 remains of " pelagic ''* organisms that have slowly fallen 



* Here we are using the word in the sense used by naturalists. 

 Under the designation " pelagic " may be included those f'onns of life 

 which lialiitually jjass tlieir existence on tlic free expanse of the 

 ocean, and which only on accidental occasions, if at all, visit the 

 continental borders, or descend (while alive) to the floor of the sea. 

 Messrs. Murray and Eenard use the word in a geological or geo- 

 gi'aphieal sense by applying it to those deep sea deposits which are for the 

 most part formed either of " pelagic " organisms, or of minute mineral 

 liarticles, such as floating pumice and fine volcanic dust, which, inas- 

 much as they are universally distributed over tlie surface waters of 

 the ocean, may in one sense be also called pelagic. We would, how- 

 ever, point out tliat it is ojien (o question how far it is wise to confuse 

 the clear and obvious distiinction between what is derived from the 

 land and what is derived from the sea. Would it not have been 

 better to place the red clay with terrigenous deposits ? Tliey admit 

 that its jnineral particles have for the most part a volcanic origin, but 

 M. Renard is inclined to believe that t]iey are due more to submarine 

 eruptions than to the eruptions of land volcanoes. That is a question 

 not yet settled; but surely the word " terrigenous' still api^lics in 

 eitlier ease. If the volcano happens to be a submarine one, that is an 

 accident, but it still belongs to the earth rather than to the sea. We 

 should prefer to sec the word " pelagic " reserved entirely for the 

 organic oozes which are truly born of the sea. Particles of \oleanic 

 dust and crystals of volcanic minerals, howe\er long tlicy may Imve 

 been floating about in the sea, are hardly entitled to the term " pelagic." 

 The sea does noi produce them ; so we prefer to consider tliem terri- 

 genous. The dead body of a sailor floating on the sea, or lying on the 

 ocean bed, could hardly be considered a " pelagic organism," e\en if 

 it had been shot out of a submarine volcano I Moreover, it is admitted 

 by the authors that " colloid clayey matter from land may play some 

 part in the formation of red clay." This is rather an important 

 question, on which we shall say more presently, but the admission 

 tends to confirm our criticism. Or if, for some reasons, this deposit 

 should appear out of place in the terrigenous group, why not form a 



from the ocean surface, together with some that live 

 on the sea floor. These have received different names, 

 according to the nature of the different organisms of 

 which they are largely composed. Sometimes they are 

 principally composed of the shells of foraminifera, sometimes 

 of the frustules of diatoms, sometimes of radiolaria ; and 

 so we have globigerina ooze (taking its name from one of 

 the foraminifera, iiliihi;/riina hulloidcs, which so largely 

 predominates), diatom ooze, radiolariau ooze, and so on. 



lied Claji is the most widely distributed and the most 

 characteristic of all the deep sea deposits (see Chart I., 

 page 44). It covers more than a quarter of the globe's 

 surface. In the Atlantic there are only four patches of it 

 of any great size, but more than half the floor of the Pacific 

 is covered by it. On looking at Chart II. the reader will 

 see that it is spread over the greater depths of the ocean 

 remote from land. In the Challeui/cr report seventy samples 

 are described. These ranged in depth from 2225 to 3950 

 fathoms ; average depth, 2730 fathoms. Ever since the 

 red clay was first discovered by the Chnllenr/cr naturalists 

 in depths over 2500 fathoms there has been much discus- 

 sion and speculation on the subject. Before the present, 

 and perhaps true, theory of its origin was formed, two 

 other views were put forward. As the reader is probably 

 aware, the present theory, due to Mr. -lohn Murray, is that 

 this clay is chiefly derived from the decomposition of 

 volcanic products. Its red colour is due to the formation 

 of ferric oxide and peroxide of manganese from decom- 

 posing volcanic material. The rate at which it grows is 

 very much slower than that at which the organic oozes 

 form, and microscopic examination has revealed the 

 interesting fact that cosmic dust from meteorites is one of 

 its constituents. The first theory of the red clay was this : 

 that it is the ultimate product produced by the disin- 

 tegration of the land — the most finely divided material — 

 which, held in suspension in sea-water, was distributed to 

 great distances by ocean currents. Though this theory 

 has been abandoned there seems to be some truth in it 

 after all ; for even Messrs. Murray and Eenard admit that 

 some small part of the red clay may be land-derived, or 

 terrigenous. Prof. J. W. Judd, whom we recently con- 

 sulted on the subject, thinks that this view may be partly 

 true, and that at present it is impossible to determine how 

 much of the deposit comes from the chemical alteration of 

 fine volcanic dust, kc. It may be, after all, that the laud- 

 derived debris plays an important part, and that the authors 

 of the report attribute too much importance to the volcanic 

 material. 



The second theory may be thus stated : in 1874 Wyville 

 Thomson expressed the opinion that the red clay was 

 primarily of organic origin, being essentially the insoluble 

 residue of calcareous organisms forming the globigerina 

 ooze. But this explanation had to be abandoned because 

 there is no evidence that pure and clean foraminiferal shells 

 contain any appreciable proportion of such mineral matter. 

 It is well known that the surface waters over those deeper 

 parts of the ocean where red clay is found contain an 

 abundance of foraminifera ; but these, as we shall see 

 later on, are dissolved in sinking through the deeper 

 waters where there is more carbonic acid in the water. 

 This is clearly proved, because the globigerina oozes gradu- 

 ally pass, as the depth becomes greater, into red clay ; and 



transition or intermediate group for it ? It is by no means free from 

 organic remains, and in some cases 20 per cent, of it is composed of 

 foraminifera. while radiolaria often form so much of it that it passes 

 into a " radiolariau ooze." Sharks' teeth, ear-bones of whales, 

 fragments of eehinoderms, mollusca, &e., are often met with in 

 considerable abundance; still the mineral, as distinguished from 

 organic particles, are its chief feature. 



