Vol. 67.] ANNIVERSARY ADDRESS OF THE PRESIDENT. XCi 



reptiles during Mesozoic times, and in the second place of the 

 rapid diminution of these forms and their replacement by mammals 

 in the Tertiary Era. The first he attributed largely to the peculiar 

 physical features which characterised the Mesozoic geography, the 

 second to the remarkable changes in these features initiated by 

 the Tertiary revolution. Although the exact conditions of physio- 

 graphy which were postulated by the author will hardly stand in 

 the light of our present knowledge of these geographies, the essay 

 is of extraordinary interest and importance in, thus early, directing 

 attention to the bearing of physical changes on problems of the 

 evolution of life. 



The earth's surface is the theatre of two types of change : — Those 

 which are external and comprise chiefly the influence of the sun 

 upon the air, land, and water ; and those which are internal and 

 depend on earth-movement. The last may be attributable entirely 

 to the activity of the interior, or possibly may be in part due to the 

 influence of external bodies, such as the sun and moon, as well. To 

 a large extent these two sets of influences must be independent. 

 We can grasp the possibility of a world's population evolving under 

 the influence of either of these suites of conditions acting in the 

 absence of the other. Eut, if the two are acting together, the 

 results will become of a much more highly complex character, 

 because with two independently acting variables there must neces- 

 sarily be periods of coincidence and of interference in the effects 

 produced. 



We should expect, in these circumstances, that epochs of relative 

 acceleration and retardation of evolution would occur with a 

 certain amount of apparent irregularity in period, complicating 

 very considerably the otherwise steadfast advance in life. 



Such striking differences as the outline, trend, contour-plan, and 

 latitudinal extension of the New World in contrast with the 

 Eurasian continent ; or the remarkable difference between the 

 Atlantic and Pacific Oceans in their coasts, depths, and structures, 

 will illustrate my meaning. And we have to recognise that differ- 

 ences probably as marked as these have swept over the places 

 now occupied by single continents and oceans in different stages of 

 their history. 



In the distribution of animals and plants at the present day 

 there is found recorded many of the physical changes that the 

 lands which they have inhabited have undergone. Is it too much 

 to hope that we may one day recognise, stored up in the organi- 

 sation of the creatures themselves, and in their ancestral history 



