THE FLOOR OF THE OCEAN 21 



important and conspicuous constituent of the one, while 

 they are merely found here and there when looked for 

 embedded in the other. The rate of accumulation of all 

 other constituents is so slow as to leave a layer of teeth 

 and ear-bones uncovered, or covered by so thin a deposit 

 that the dredge can collect them freely. Sir John 

 Murray calculates that only a few inches of this deposit 

 have accumulated since the Tertiary Period. These 

 most interesting facts prove furthermore that the great 

 ocean basins and continental areas have occupied the 

 same relative positions since the formation of the first 

 stratified rocks ; for no oceanic deposits are found any- 

 where in the latter. We know the sources of the oceanic 

 deposit, and it might be possible to form an estimate, 

 within wide limits, of its rate of accumulation. If it were 

 possible to ascertain its thickness by means of a boring, 

 some conclusions as to the time which has elapsed during 

 the lifetime of certain species perhaps even the lifetime 

 of the oceans themselves might be arrived at. Lower 

 down the remains of earlier species would probably be 

 found. The depth of this deposit and its character at 

 deeper levels are questions of overwhelming interest; 

 and perhaps even more so is the question as to what lies 

 beneath. Long before the Challenger had proved the 

 persistence of oceanic and continental areas, Darwin, 

 with extraordinary foresight, and opposed by all other 

 naturalists and geologists, including his revered teacher, 

 Lyell, had come to the same conclusion. His reasoning 

 on the subject is so convincing that it is remarkable that 

 he made so few converts, and this is all the more sur- 

 prising since the arguments were published in the Origin 

 of Species, which in other respects produced so profound 

 an effect. In speculating as to the rocks in which the 

 remains of the ancestors of the earliest known fossils may 

 still exist, he suggested that, although the existing relation- 

 ship between the positions of our present oceans and 

 continental areas is of immense antiquity, there is no 

 reason for the belief that it has persisted for an indefinite 

 period, but that at some time long antecedent to the 

 earliest known fossiliferous rocks 'continents may have 



