134 



NA TURE 



[ June 5. 1884 



posits of the abysmal areas of the ocean basins from the series of 

 rocks in the geological formations. As regards the vast deposits 

 of red clay, with its manganese concretions, its zeolites, cosmic 

 dust, and remains of Vertebrates, and the organic oozes which 

 are spread out over the bed of the Central Pacific, Atlantic, and 

 Indian Oceans, have they their analogues in the geological series 

 of rocks ? If it be proved that in the sedimentary strata the 

 pelagic sediments are not represented, it follows that deep and 

 extended oceans like those of the present day cannot formerly 

 have occupied the areas of the present continents, and as a 

 corollary the great lines of the ocean basins and continents must 

 have been marked out from the earliest geological ages. We 

 thus get a new confirmation of the opinion of the permanence of 

 the continental areas. 



But without asserting in a positive manner that the terrestrial 

 areas and the areas covered by the waters of the great ocean 

 basins have had their main lines marked out since the commence- 

 ment of geological history, it is, nevertheless, a fact, proved by 

 the evidence derived from a study of the pelagic sediments, that 

 these areas have a great antiquity. The accumulation of sharks' 

 teeth, of the ear-bones of Cetaceans, of manganese concretions, 

 of zeolites, of volcanic material in an advanced state of decom- 

 position, and of cosmic dust, at points far removed from the 

 continents, tend to prove this. There is no reason for supposing 

 that the parts of the ocean where these Vertebrate remains are 

 found are more frequented by sharks or Cetaceans than other 

 regions where they are never or only rarely dredged from the 

 deposits at the bottom. When we remember also that these 

 ear-bones, teeth of sharks, and volcanic fragments, are some- 

 times incrusted with two centimetres of manganese oxide, while 

 others have a mere coating, and that some of the bones and 

 teeth belong to extinct species, we may conclude with great cer- 

 tainty that the clays of these oceanic basins have accumulated 

 with extreme slowness. It is indeed almost beyond question 

 that the red clay regions of the Central Pacific contain accumu- 

 lations belonging to geological ages different from our own. 

 The great antiquity of these formations is likewise confirmed in 

 a striking manner by the presence of cosmic fragments, the 



nature of which we 1 id (" On Cosmic and Volcanic 



Dust," Proc. Roy. Sec. EJiit.). In order to account for the 

 accumulation of all the substances in such relatively great abun- 

 dance in the areas where they were dredged, it is necessary to 

 suppose the oceanic basins to have remained the same for a vast 

 period of time. 



The sharks' teeth, ear-bones, manganese nodules, altered 

 volcanic fragments nic dust are met with in 



greatest abundano clays of the Central Pacific, at 



that point on the earths surface farthest removed from conti- 

 nental land. They are 1' 1 in the Radiola 

 are rare in the Globigerina, l>iatom, and 1'teropod oozes, and 

 they have been dredged only in a few instances in the terrigenous 

 .mi e- are present in all 

 the deposits, bul 1 abundance of other matters in 

 the more rapidly forming deposits their presence is masked, and 

 the chance of dredging them is reduced. We may then regard 

 the greater or less abundance of these materials, which are so 

 characteristic of a true red clay, as beii of the rela- 

 tive rate of accumulation of the marine sediments in which they 

 lie. The terrigenous deposits accumulate most rapidly, then 

 follow in order Pteropod ooze, ' llobigi rina ooze, I fiatom ooze, 

 Radiolarian ooze, and, slowest of all, red clay. 



From the data now advanced, it appears possible to deduce 

 other conclusions important from a geological point of view. In 

 the deposits due essentially to the action of the ocean, we are at 

 once struck by the great variety <>t sediments which may accu- 

 mulate in re llie external conditions are almost 

 identical. Again, marine faunas and floras, at least those of the 

 surface, differ greatly, both with respect to species and to relative 

 abundance of individuals, in different regions of the ocean ; and 

 as their remains determine the character of the deposit in many 

 instances, it is legitimate to conclude that the occurrence of 

 organisms of a different nature in several beds is not an argu- 

 ment against the synchronism of tin layers which contain them. 

 The small extent occupied by littoral formations, especially 

 those of an arenaceous nature, shown by our investigations, and 

 the relatively slow rate at which such deposits are formed all mg 

 a stable coast, are matters of importance. 



In the present state of things there does not appear to be any- 

 thing to account for the enormous thickness of the clastic sedi- 

 ments making up certain geological formations, unless we 



consider the exceptional cases of erosion which are brought into 

 play when a coast is undergoing constant elevation or subsidence. 



Great movements of the land are doubtless necessary for the 

 formation of thick beds of transported matter like sandstones and 

 conglomerates. 



In this connection may be noted the fact that in certain regions 

 of the deep sea no appreciable formation is now taking place. 

 Hence the absence, in the sedimentary series, of a layer repre- 

 senting a definite horizon must not always be interpreted as 

 proof either of the emergence of the bottom of the sea during the 

 corresponding period, or of an ulterior erosion. Arenaceous 

 formations of great thickness require seas of no great extent and 

 coasts subject to frequent oscillations, which permit the shores to 

 advance and retire. Along these, through all periods of the 

 earth's history, the great marine sedimentary phenomena have 

 taken place. 



The continental geological formations, when compared with 

 marine deposits of modern seas and oceans, present no analogues 

 to the red clays, Radiolarian, Globigerina, Pteropod, and Diatom 

 oozes. On the other hand, the terrigenous deposits of our lakes, 

 shallow seas, inclosed seas, and the shores of the continents, 

 reveal the equivalents of our chalks, greensands, sandstones, con- 

 glomerates, shales, marls, and other sedimentary formations. 

 Such formations as certain Tertiary deposits of Italy, Radiolarian 

 earth from Barbados, and portions of the Chalk where pelagic 

 conditions are indicated, must be regarded as having been laid 

 down rather along the border of a continent than in a true 

 oceanic area. On the other hand, the argillaceous and calcareous 

 rocks recently discovered by Dr. Guppy in the upraised coral 

 islands in the Solomon Group are nearly identical with the 

 Pteropod and Globigerina oozes of the Pacific. 



Regions situated similarly to inclosed and shallow seas and the 

 borders of the present continents appear to have been, through- 

 out all geological ages, the theatre of the greatest and most 

 remarkable changes ; in short, all, or nearly all, the sedimentary 

 rocks of the continents would seem to have been built up in 

 areas like those now occupied by the terrigenous deposits, which 

 we may designate " the transitional or critical area of the earth's 

 surface." This area occupies we estimate, about two-eighths of 

 the earth's surface, while the continental and abysmal areas 

 occupy each about three-eighths. 



During each era of the earth's history the borders of some 

 lands have sunk beneath the sea and been covered by marine 

 sediments, while in other parts the terrigenous deposits have 

 ited into dry land, and have carried with them a record 

 which nourished in the sea of the time. In this 

 transitional area there has been throughout a continuity of geo- 

 ii' I biological phenomena. 

 Iiese considerations it will be evident that the character 

 of a deposit is determined much more by distance from the 

 shore of a continent than by actual depth ; and the same would 

 appear to be the case with respect to the fauna spread over the 

 floor of the present oceans. Dredgings near the shores of con- 

 tinent-., in depths of 1000, 2;oo, or 3000 fathoms, are more pro- 

 ductive both in species and individuals than dredgings at similar 

 oral hundred miles seawards. Again, among the few 

 inthe abysmal areas furthest removed from land, 

 tlie majority show archaic characters, or belong to groups which 

 have a wide distribution in time as well as over the floor of the 

 ; enl hi-. Such are the llexaetinellida, Brachiopoda, 

 moiIs and other Echinoderms, &c. 



As already mentioned, the transitional area is that which now 

 shows the gi eatest variety in respect to biological and physical 

 conditions, and in past time it has been subjeel to the most 

 frequent and the greatest amount of change. The animals now 

 living in this area may be regarded as the greatly modified 

 descendants of those which have lived in similar regions in past 

 geological ages, and some of whose ancestors have been pre- 

 served in the sedimentary rocks as fossils. On the other hand, 

 many of the animals dredged in the abysmal regions are most 

 probably also the descendants of animals which lived in the 

 shallower water- of former geological periods, but descended 

 into deep water to escape the severe struggle for existence which 

 niu-t always have obtained in those depths affected by light, 

 lieat, motion, and other conditions. Having found existence 

 possible in the less favourable and deeper water, they may be 

 regarded as having slowly spread themselves over the floor of tire 

 ocean, but without undergoing great modifications, owing to 

 the extreme uniformity of the conditions and the absence of com- 

 petition. Or we may suppose that, in the depressions which 



