81 

THE DISTRIBUTION AND DISPERSAL 
OF ANIMALS. 
By CHARLES OLDHAM. 14th November, 1905. 
If all the closely related species of animals or plants which 
form a natural group or genus have been derived by descent with 
modification from some single pre-existing species, then a 
rational explanation must be given of their distribution over the 
surface of the globe. If no feasible explanation is forthcoming, 
then the doctrine of evolution cannot be considered proved or 
even probable. 
So long as the permanence of species was a generally accepted 
doctrine, the geographical distribution of animals had little 
interest for naturalists, but when once Darwin’s epoch-making 
theory was propounded, the subject became fraught with meaning 
and interest thereto unsuspected. 
Physicists and Geologists are agreed that, roughly speaking, 
the great continental land-masses of the world are extremely 
ancient, if not primeval, features of its surface. ‘The land area 
of our globe is rather less than one-third of its total; the re- 
mainder being occupied by the great oceans. It has been 
calculated that if the solid matter of the earth’s crust were 
reduced to one level, it would be covered everywhere by water, 
to the depth of some two miles. In the life of this old world 
it is only. to-day and yesterday that Great Britain and Ireland 
have been separated from the Continent of Kurope, while the day 
before yesterday, so to speak, this country was submerged to such 
a depth that only the tops of our highest mountains protruded 
as islands above the sea. Careful study in that oldest of all 
libraries, whose volumes are the fogsil-bearing rocks, proves 
