104 EXPEDITION OF THE "CHALLENGER" in 



are not only " temporis" but " mice filice " ; and, 

 consequently, that the time during which life has 

 been active on the globe may be indefinitely 

 greater than the period, the commencement of 

 which is marked by the oldest known rocks, 

 whether fossiliferous or unfossiliferous. 



And thus we are led to see where the solution 

 of a great problem and apparent paradox of 

 geology may lie. Satisfactory evidence now exists 

 that some animals in the existing world have been 

 derived by a process of gradual modification from 

 pre-existing forms. It is undeniable, for example, 

 that the evidence in favour of the derivation of 

 the horse from the later tertiary Hipparion, and 

 that of the Hipparion from Anchitherium, is as 

 complete and cogent as such evidence can reason- 

 ably be expected to be ; and the further investiga- 

 tions into the history of the tertiary mammalia are 

 pushed, the greater is the accumulation of evidence 

 having the same tendency. So far from palae- 

 ontology lending no support to the doctrine of 

 evolution as one sees constantly asserted that 

 doctrine, if it had no other support, would have 

 been irresistibly forced upon us by the palaeonto- 

 logical discoveries of the last twenty years. 



If, however, the diverse forms of life which now 

 exist have been produced by the modification of 

 previously-existing less divergent forms, the recent 

 and extinct species, taken as a whole, must fall 

 into series which must converge as we go back in 



