1880.] on Land and Sea in relation to Geological Time. 209 



existing ou the tlocp-sca bed so nearly represent Cretaceous types 

 supposed to have long since become extinct, that wo may fiiirly 

 suppose them to be their lineal descendants. Hence, I went on to 

 say, " the question of the continuity of ' descent with modification ' 

 will probably receive more elucidation from the study of the Deep-sea 

 Fauna, than from any other line of scientific inquiry." This 

 anticipation, also, is in course of complete fulfilment. An enormous 

 amount of Zoological material has been carefully collected from 

 various parts of the great Oceanic area, and at depths ranging down- 

 wards to from three to five miles ; and this is being studied, with a 

 view to all the determinations I have indicated, by Naturalists of the 

 highest competency in their respective departments. The results of 

 this part of the inquiry have so far been only disappointing to those 

 who had somewhat unreasonably expected that, because Cretaceous 

 types had been found still living in the deep seas of our part of tho 

 globe, the Ammonites of the Secondary period, and even the Trilobites 

 of the Palaeozoic, might be lurking in abyssal depths elsewhere, — an 

 expectation which I never myself shared. 



But whilst the past history of Animal Life on our globe will 

 doubtless receive all the new light which I had anticipated from the 

 scientific study of the ' Challenger ' collection, an unexpected clue 

 has been found in the examination of the sediments now in process 

 of deposition on the Ocean-bottom, to the solution of a question in 

 Physical Geology, second to none in importance and interest, which I 

 propose now to bring before you. 



Every tyro in Geology knows it to be a fact not admitting of a 

 doubt, that all our existing Land has at some period or other been 

 under the sea ; and the converse proposition — that every part of the 

 Sea-bottom has at some period or other risen above the surface — 

 has been very generally accepted, even by geologists of the highest 

 eminence. Thus Sir Charles Lyell, in his chapters on the vicissitudes 

 in Climate caused by geographical changes, assumed it as a fact 

 beyond dispute, not only "that every part of the space now covered by 

 the deepest ocean has been land," but even that " the bed of the ocean 

 has been lifted up to the height of the loftiest mountains ; " and con- 

 sidered it proved that " if we had a series of maps, in which restora- 

 tions of the physical geography of thirty or more periods were de- 

 picted, they would probably bear no more resemblance to each other, 

 or to the actual position of land and sea, than does the map of one 

 hemisphere bear to that of the other." — These statements, I may 

 remark, are repeated without any qualification in the twelfth chapter 

 of the latest edition of his masterly ' Principles ' ; notwithstanding 

 that towards the conclusion of the same chapter, he distinctly recog- 

 nized the enormous disproportion between the average elevation of 

 the Land and the average depth of the Ocean-basins, whereby, while a 

 vertical depression of 1000 feet would submerge a large part of the 

 present continental land, a vertical elevation of from twelve to fifteen 



