TRANSACTIONS OF SECTION C. 727 
of geology and paleontology, and affirm that unless the deductions we draw from 
that evidence can be disproved, we are entitled to maintain them as entirely borne 
out by the testimony of the rocks. 
Until, therefore, it can be shown that geologists and paleontologists have mis- 
interpreted their records, they are surely well within their logical rights in claiming 
as much time for the history of this earth as the vast body of evidence accumulated 
by them demands. So far as I have been able to form an opinion, one hundred 
millions of years would suffice for that portion of the history which is registered in 
the stratified rocks of the crust. But if the palzeontologists find such a period too 
narrow for their requirements, I can see no reason on the geological side why they 
should not be at liberty to enlarge it as far as they may find to be needful for the 
evolution of organised existence on the globe. As I have already remarked, it is 
not the length of time which interests us so much as the determination of the 
relative chronology of the events which were transacted within that time. As to 
the general succession of these events, there can be no dispute. We have traced 
its stages from the bottom of the oldest rocks up to the surface of the present con- 
tinents and the floor of the present seas. We know that these stages have followed 
each other in orderly advance, and that geological time, whatever limits may be 
assigned to it, has sufficed for the passage of the long stately procession. 
‘We may, therefore, well leave the dispute about the age of the earth to the 
decision of the future. In so doing, however, I should be glad if we could carry 
away from it something of greater service to science than the consciousness of 
having striven our best in a barren controversy, wherein concession has all to be on 
one side and the selection of arguments entirely on the other. During these years 
of prolonged debate I have often been painfully conscious that in this subject, as in 
so many others throughout the geological domain, the want of accurate numerical 
data is a serious hindrance to the progress of our science. Heartily do I acknow- 
ledge that much has been done in the way of measurements and experiments for 
the purpose of providing a foundation for estimates and deductions. But infinitely 
more remains to be accomplished. The field of investigation is almost boundless, 
for there is hardly a department of geological dynamics over which it does not 
extend. The range of experimental geology must be widely enlarged, until every 
process susceptible of illustration or measurement by artificial means has been 
investigated. Field-observation needs to be supplemented where possible by 
instrumental determinations, so as to be made more precise and accurate, and more 
capable of furnishing reliable numerical statistics for practical as well as theoretical 
deductions. 
The subject is too vast for adequate treatment here. But let me illustrate my 
meaning by selecting a few instances where the adoption of these more rigid 
methods of inquiry might powerfully assist us in dealing with the rates of geo- 
logical processes and the value of geological time. Take, for example, the wide 
range of lines of investigation embraced under the head of Denudation. So 
voluminous a series of observations has been made in this subject, and so ample is 
the literature devoted to it, that no department of geology, it might be thought, 
has been more abundantly and successfully explored. Yet if we look through the 
pile of memoirs, articles, and books, we cannot but be struck with the predominant 
vagueness of their statements, and with the general absence of such numerical 
data determined by accurate, systematic, and prolonged measurement as would 
alone furnish a satisfactory basis for computations of the rate at which denudation 
takes place. Some instrumental observations of the greatest value have indeed 
been made, but, for the most part, observations of this kind have been too meagre 
and desultory. 
A little consideration will show that in all branches of the investigation of 
denudation opportunities present themselves on every side of testing, by accurate 
instrumental observation and measurement, the rate at which some of the most 
universal processes in the geologival régime of our globe are carried on. 
It has long been a commonplace of geology that the amount of the material 
removed in suspension and solution by rivers furnishes a clue to the rate of denu- 
dation of the regions drained by the rivers, But how unequal in value, and 
