n6 



NA TURE 



{May 29, 1884 



( Red clay, 



_ , . Globigerina ooze, 



Pelagic ) r,. ° , 



, a -. , Pteropod ooze, 



deposits. Diatonl oze, 



v Radiolarian ooze, 



Found in the 



abysmal regions 



of the ocean 



basins. 



Geographical and Bathymetrical Distribution. — In the pre- 

 ceding pages we have confined our remarks essentially to the 

 lithological nature of the deep-sea deposits, including in this 

 term the dead shells and skeletons of organisms. From this 

 point of view it has been possible to define the sediments and to 

 give them distinctive names. We now proceed to consider their 

 geographical and bathymetrical distribution, and the relations 

 which exist between the mineralogical and organic composition 

 and the different areas of the ocean in which they are formed. 



A cursory glance at the geographical distribution -hows that 

 the deposits which we have designated MUDS and SANDS are 

 situated at various depths at no great distance from the land, 

 while the organic oozes and red clays occupy the abysmal 

 regions of the ocean basins far from land. Leaving out of view the 

 coral and volcanic muds and sands which are found principally 

 around oceanic islands, we notice that our blue muds, green muds 

 and sands, red muds, together with all the coast and shore forma- 

 tions, are situated along the margins of the continents and in 

 inclosed and partially inclosed seas. The chief characteristic of 

 these deposits is the presence in them of continental debris. 

 The blue muds are found in all the deeper parts of the regions 

 just indicated, and especially near the embouchures of rivers. 

 Red muds do not differ much from blue muds except in colour, 

 due to the presence of ferruginous matter in great abundance, 

 and we find them under the same conditions as the blue muds. 

 The green muds and sands occupy, as a rule, portions of the 

 coast where detrital matter from rivers is not, apparently, accu- 

 mulating at a rapid rate, viz. on such places as the Agulhas 

 Bank, off the east coast of Australia, off the coast of Spain, and 

 at various points along the coast of America. 



Let us cast a glance at the region occupied by terrigenous 

 deposits, in which we include all truly littoral formations. This 

 region extends from high-water mark clown, it may be, to a 

 depth of over four miles, and in a horizontal direction from 60 

 to perhaps 300 miles seawards, and includes, in the view we 

 take, all inland seas, such as the North Sea, Norwegian Sea, 

 Mediterranean Sea, Red Sea, China Sea, Japan Sea, Caribbean 

 Sea, and many others. It is the region of change and of variety 

 with respect to light, temperature, motion, and biological condi- 

 tions. In the surface waters the temperature ranges from 8o° F. 

 in the tropics, to 28° F. in the polar regions. Below the surface 

 down to the nearly ice-cold water found at the lower limits of 

 the region in the deep sea. there is in the tropics an equally great 

 range of temperature. Plants and animals are abundant near the 

 shore, and animals extend in relatively great abundance down to 

 the lower limits of this region which is now covered by these 

 terrigenous deposits. The specific gravity of the water varies 

 much, owing to mixture with river water or great local evapora- 

 tion, and this variation in its turn affects the fauna and flora. In 

 the terrigenous region tides and currents produce their maximum 

 effect, and these influences can in some instances be traced to a 

 depth of 300 fathoms, or nearly 2000 feet. The upper or con- 

 tinental margin of the region is clearly defined by the high-water 

 mark of the coast-line, which is constantly changing through 

 breaker action, elevation, and subsidence. The lower or abysmal 

 margin is less clearly marked out. It passes in most cases in- 

 sensibly into the abysmal region, but may be regarded as ending 

 when the mineral particles from the neighbouring continents 

 begin to disappear from the deposits, which then pass into an 

 organic ooze or a red clay. 



Contrast with these, those conditions which prevail in the 

 abysmal region in which occur the organic oozes and red clay, 

 the distribution of which will presently be considered. This 

 area comprises vast undulating plains from two to five miles 

 beneath the surface of the sea, the average being about three 

 miles, here and there interrupted by hugi volcanic cones (the 

 oceanic islands). No sunlight ever reaches these deep cold 

 tracts. The range of temperature over them is not more than 7°, 

 viz. from 31° to 38^ F., and is apparently constant throughout 

 the whole year in each locality. Plant life is absent, and 

 although animals belonging to all the great types are present, 

 there is no great variety of form or abundance of individuals. 

 Change of any kind is exceedingly slow. 



What is the distribution of deposits in this abysmal region 



of the earth's surface? In the tropical and temperate zones 

 of the great oceans, which occupy about 1 10° of latitude 

 between the two polar zones, at depths where the action 

 of the waves is not felt, and at points to which the terrigenous 

 materials do not extend, there are now forming vast accumula- 

 tions of Globigerina and other pelagic Foraminifera, coccoliths, 

 rhabdoliths, shells of pelagic Mollusks, and remains of other 

 organisms. These deposits may perhaps be called the sediments 

 of median depths and of wanner zones, because they diminish 

 in great depths and tend to disappear towards the poles. This 

 fact is evidently in relation with the surface temperature of the 

 ocean, and shows that pelagic Foraminifera and Mollusks live in 

 the superficial waters of the sea, whence their dead shells fall to 

 the bottom. Globigerina ooze is not found in inclosed seas nor 

 in polar latitudes. In the Southern Hemisphere it has not been 

 met with beyond the 50th parallel. In the Atlantic it is de- 

 posited upon the bottom at a very high latitude below the warm 

 waters of the Gulf Stream, and is not observed under the cold 

 descending polar current which runs south in the same latitude. 

 These facts are readily explained, if we admit that this ooze is 

 formed chiefly by the shells of surface organisms, which require 

 an elevated temperature and a wide expanse of sea. But as long 

 as the conditions of the surface are the same, we would expect 

 the deposits at the bottom also to remain the same. In showing 

 that such is not the case, we are led to take into account an 

 agent which is in direct correlation with the depth. We may 

 regard it as established that the majority of the calcareous or- 

 ganisms which make up the Globigerina and Pteropod oozes 

 live in the surface waters, and we may also take for granted that 

 there is always a specific identity between the calcareous organisms 

 which live at the surface and the shells of these pelagic creatures 

 found at the bottom. This observation will permit us to place 

 in relation the organic deposits and those which are directly or 

 indirectly the result of the chemical activity of the ocean. Globi- 

 gerina ooze is found in the tropical zone at depths which do not 

 exceed 2400 fathoms, but when depths of 3000 fathoms are 

 explored in this zone of the Atlantic and Pacific, there is found 

 an argillaceous deposit without, in many instances, any trai e ol 

 calcareous organisms. When we descend from the "submarine 

 plateaus " to depths which exceed 2250 fathoms, the Globigerina 

 ooze gradually disappears, passing into a grayish marl, and finally 

 is wholly replaced by an argillaceous material which covers the 

 bottom at all depths greater than 2900 fathoms. 



The transition between the calcareous formations and the 

 argillaceous ones takes place by almost insensible degrees. The 

 thinner and more delicate shells disappear first. The thicker 

 and larger shells lose little by little the sharpness of their contour 

 and appear to undergo a profound alteration. They assume a 

 brownish colour, and break up in proportion as the calcareous 

 constituent disappears. The red clay predominates more and 

 more as the calcareous element diminishes in the deposit. 



If we now recollect that the most important elements of the 

 organic deposits have descended from the superficial waters, and 

 that the variations in contour of the bottom of the sea cannot of 

 themselves prevent the debris of animals and plants from 

 accumulating upon the bottom, their absence in the red clay 

 areas can only be explained by a decomposition under the action 

 of a cause which we must seek to discover. 



Pteropod ooze, it will be remembered, is a calcareon 

 organic deposit, in which the remains of Pteropods and other 

 pelagic Mollusca are present, though they do not always form a 

 preponderating constituent, and it has been found that their 

 presence is in correlation with the bathymetrical distribution. 



In studying the nature of the calcareous elements which are 

 deposited in the pelagic areas, it has been noticed that, like the 

 shells of the Foraminifera, those of the Thecosomatous Pteropoda, 

 which live everywhere in the superficial waters, especially in the 

 tropics, become fewer in number as the depth from which the 

 sediments are derived increases. We have just observed that 

 the shells of Foraminifera disappear gradually as we descend 

 along a series of soundings from a point where the Globigerina 

 ooze has abundance of carbonate of lime, towards deeper 

 regions; but we notice also that when the sounding-rod brings 

 tip 1 graduated series of sediments from a declivity descending 

 into deep water, among the calcareous shells those of the Ptero- 

 pods and Heteropods disappear first in proportion as the depth in- 

 \ depths less than 1400 fathoms in the tropics a Pteropod 

 ooze is found with abundant remains of Heteropods and Ptero- 

 pods ; deepei soundings then give a Globigerina ooze without these 

 molluscan remains ; and in still greater depths, as before men- 



