724 REPORT—1899. 
theories which appear to demand longer periods of time than those which now 
appear allowable.’ ? 
This ‘ wrong,’ which Professor Darwin so seriously deprecated, has been com- 
mitted not once, but again and again, in the history of this discussion. Lord 
Kelvin has never taken any notice of the strong body of evidence adduced by 
geologists and paleontologists in favour of a much longer antiquity than he is 
now disposed to allow for the age of the earth. His own three physical arguments 
have been successively re-stated, with such corrections and modifications as he has 
found to be necessary, and no doubt further alterations are in store for them. He 
has cut off slice after slice from the allowance of time which at first he was pre- 
pared to grant for the evolution of geological history, his latest pronouncement 
being that ‘it was more than twenty and less than forty million years, and 
probably much nearer twenty than forty.’* But in none of his papers is there an 
admission that geology and paleontology, though they have again and again raised 
their voices in protest, have anything to say in the matter that is worthy of 
consideration. 
It is difficult satisfactorily to carry on a discussion in which ycur opponent 
entirely ignores your arguments, while you have given the fullest attention to his. 
In the present instance, geologists have most carefully listened to all that has been 
brought forward from the physical side. Impressed by the force of the physical 
reasoning, they no longer believe that they can male any demands they may please 
on past time. They have been willing to accept Lord Kelvin’s original estimate 
of 100 millions of years as the period within which the history of life upon the 
planet must be comprised ; while some of them have even sought in various ways 
to reduce that sum nearer to his lower limit, Yet there is undoubtedly a preva- 
lent misgiving, whether in thus seeking to reconcile their requirements with the 
demands of the physicist they are not tying themselves down within limits of 
time which on any theory of evolution would have been insufficient for the 
development of the animal and vegetable kingdoms. 
It is unnecessary to recapitulate before this Section of the British Association, 
even in briefest outline, the reasoning of geologists and paleontologists which 
leads them to conclude that the history recorded in the crust of the earth must 
have required for its transaction a much vaster period of time than that to which 
the physicists would now restrict it.* Let me merely remark that the reasoning 
is essentially based on observations of the present rate of geological and biological 
changes upon the earth’s surface. It is not, of course, maintained that this rate 
has never varied in the past. But it is the only rate with which we are familiar, 
which we can watch and in some degree measure, and which, therefore, we can 
take as a guide towards the comprehension and interpretation of the past history 
of our planet. 
It may be, and has often been, said that the present scale of geological and 
biological processes cannot be accepted as a reliable measure for the past. Start- 
ing from the postulate, which no one will dispute, that the total sum of terrestrial 
energy was once greater than it is now and has been steadily declining, the 
physicists have boldly asserted that all kinds of geological action must have been 
more vigorous and rapid during bygone ages than they are to-day ; that volcanoes 
were more gigantic, earthquakes more frequent and destructive, mountain-upthrows 
more stupendous, tides and waves more powerful, and commotions of the atmo- 
sphere more violent, with more ruinous tempests and heavier rainfall. Assertions 
of this kind are temptingly plausible and are easily made. But it is not enough 
that they should be made; they ought to be supported by some kind of evidence 
1 Rep. Brit. Assoc. 1886, p. 518. 
2 «The Age of the Earth,’ Presidential Address to the Victoria Institute for 1897, 
p. 10; alsoin Phil. Mag. January 1899. 
3 The geological arguments are briefly given in my Presidential Address to the 
British Association at the Edinburgh Meeting of 1892. The biological arguments 
were well stated, and in some detail, by Professor Poulton in his Address to the 
Zoological Section of the Association at the Liverpool Meeting of 1896. 
