272 Proceedings of the Royal Physical Society. 
however, the case will be different. Each will be only too 
fully aware of the difficulty that is encountered in attempting 
to explain the vast and important changes in both the organic 
and the inorganic worlds during the period in question. If 
we may judge of the rate of changes in the organic world by 
the rate at which, on the whole, those changes have pro- 
ceeded since the dawn of the Historical Period, then the 
time required for the evolution of the various forms of life 
that have peopled the globe since the commencement of the 
Tertiary Period must be vast almost beyond conception. 
Again, if, as geologists, we have to interpret the changes 
in the inorganic world that have taken place in the past, we 
are bound to do so by reference to the changes that are going 
on at present, and this is especially true when we are dealing 
with the geological history of a period so comparatively 
recent as that just noticed. Not to interpret the recent past 
by the actual present would be to reject one of the surest 
and best principles of geological reasoning. Those who, 
considering all these points, may still be in doubt regarding 
the chronological importance of the Tertiary Period, may be 
reminded that in the Mediterranean basin alone an aggregate 
thickness of over 23,000 feet of strata, largely composed of 
marine limestones, was formed in this period, and that the 
very materials out of which much of our largest mountain 
chains have been shaped had not come into existence in the 
form of rocks until a late period of Tertiary times. 
Finally, if it can be shown, on sufficiently good grounds, 
that the changes that have taken place in a period so recent 
as the Tertiary Period require for their accomplishment a 
measure of time so much in excess of that which, on mathe- 
matical grounds, we are told is all that can be allowed for the 
time since it was first possible for life to exist upon the 
earth, then, I would respectfully submit, there must be some 
serious error in the data upon which those computations were 
founded. I venture to think that such must be the case, 
and in the concluding portion of this address I shall make 
bold to point out where it seems to me that some part of 
the error may possibly have crept in. In the meantime, 
geologists will probably agree with me in thinking that we 
