ANNIVERSARY ADDRESS OF THE PRESIDENT. lix 
There is nothing, then, in what is known of the older Eocene 
mammals of the Arctogeeal province to forbid the supposition that 
they stood in an ancestral relation to those of the Calcaire Grossier 
and the Gypsum of the Paris basin, and that our present fauna, 
therefore, is directly derived from that which already existed in 
Arctogeea at the commencement of the Tertiary period. But if we 
now cross the frontier between the Cainozoic and the Mesozoic 
faunz, as they are preserved within the Arctogeal area, we meet 
with an astounding change, and what appears to be a complete and 
unmistakable break in the line of biological continuity. 
Among the twelve or fourteen species of Mammalia which are 
said to have been found in the Purbecks, not one is a member of 
the orders Chiroptera, Rodentia, Ungulata, or Carnivora, which 
are so well represented in the tertiaries. No Jnsectivora are cer- 
tainly known, nor any opossum-like Marsupials. Thus there is a 
vast negative difference between the Cainozoic and the Mesozoic 
mammalian faune of Europe. But there is a still more important 
positive difference, inasmuch as all these Mammalia appear to be 
Marsupials belonging to Australian groups, and thus appertaining 
to a different distributional province from the Eocene and Miocene 
marsupials, which are Austro-Columbian. So far as the imperfect 
materials which exist enable a judgment to be formed, the same law 
appears to have held good for all the earlier Mesozoic Mammalia. 
Of the Stonesfield slate mammals, one, Amphitherium, has a defi- 
nitely Australian character; one, Phascolotherium, may be either 
Dasyurid or Didelphine ; of a third, Stereognathus, nothing can at 
present be said. The two mammals of the Trias, also, appear to 
belong to Australian groups. 
Every one is aware of the many curious points of resemblance 
between the marine fauna of the European Mesozoic rocks and that 
which now exists in Australia. But if there was this Australian 
facies about both the terrestrial and the marine faunz of Mesozoic 
Europe, and if there is this unaccountable and immense break 
between the fauna of Mesozoic and that of Tertiary Europe, is it 
not a very obvious suggestion that, in the Mesozoic epoch, the Aus- 
tralian province included Europe, and that the Arctogzeal province 
was contained within other limits? The Arctogzeal province is at 
present enormous, while the Australian is relatively small. Why 
should not these proportions have been different during the Meso- 
zoic epoch? 
Thus I am led to think that by far the simplest and most ra- 
tional mode of accounting for the great change which took place in 
the living inhabitants of the European area at the end of the Mesozoic 
epoch is the supposition that it arose from a vast alteration of 
the physical geography of the globe, whereby an area long tenanted 
by Cainozoic forms was brought into such relations with the Euro- 
pean area that migration from the one to the other became possible, 
and took place on a great scale. 
This supposition relieves us, at once, from the difficulty in which 
we were left, some time ago, by the arguments which I used to 
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