520 SCIENCE. 
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 your opponent entirely 
ignores your arguments, while you have 
given the fullest attention to his. In the 
present instance, geologists have most care- 
fully 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 make any 
demands they may please on past time. 
They have been willing to accept Lord Kel- 
vin’s original estimate of 100 millions of 
years as the period within which the his- 
tory of life upon the planet must be com- 
prised; while some of them have even 
sought in various ways to reduce that sum 
nearer to his lower limit. Yet there is un- 
doubtedly a prevalent misgiving, whether 
in thus seeking to reconcile their require- 
ments with the demands of the physicist 
they are not tying themselves down within 
limits of time which on any theory of evo- 
lution 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 
conelude 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 obser- 
* The geological arguments are briefly given in my 
Presidential Address to the British Association at the 
Edinburgh meeting of 1892. The biological argu- 
ments were well stated, and in some detail, by Pro- 
fessor Poulton in his address to the Zoological Section 
of the Association at the Liverpool Meeting of 1896. 
[N. S. Vou. X. No. 250, 
vations 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. Starting 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 as- 
serted that all kinds of geological action 
must have been more vigorous and rapid 
during bygone ages than they are to-day ; 
that voleanoes were more gigantic, earth- 
quakes more frequent and destructive, 
mountain-upthrows more stupendous, tides 
and waves more powerful, and commotions 
of the atmosphere more violent, with more 
ruinous tempests and heavier rainfall. As- 
sertions of this kind are temptingly plau- 
sible and are easily made. But it is not 
enough that they should be made; they 
ought to be supported by some kind of evi- 
dence to show that they are founded on 
actual fact and not on mere theoretical pos- 
sibility. Such evidence, if it existed, could 
surely be produced. The chronicle of the 
earth’s history, from a very early period 
down to the present time, has been legibly 
written within the sedimentary formations 
of the terrestrial crust. Let the appeal be 
made to that register. Does it lend any 
support to the affirmation that the geolog- 
ical processes are now feebler and slower 
than they used to be? If it does, the phys- 
icists, we might suppose, would gladly 
bring forward its evidence as irrefragable 
confirmation of the soundness of their con- 
Sesecida 
AE LLI e 
Semesneaa te ae Bey 
i a eae 
