2 Proceedings of the Royal Physical Society. 
to select for my address to-night any subject involving 
protracted original investigation. Under these circumstances, 
I thought it best to confine my efforts to taking a general 
view of some subject of interest alike to geologists and 
biologists, and I have therefore elected to place before 
you my views as to the present aspect and position of the 
well-known doctrine of the “ Permanence of the Ocean- 
Basins,” or, to speak more correctly, of the abysses of 
these basins. 
Even if the Science of Geology had no existence, if the 
structure of the earth’s crust were absolutely unknown to us, 
nevertheless the researches of the zoologist and botanist 
would have convinced us that the present distribution of 
land and water could by no means have existed unchanged 
since the beginning of terrestrial history. Were it otherwise 
—were the present configuration of the earth’s surface a 
matter of primordial arrangement, and immutable, then the 
innumerable problems connected with the distribution of 
animals and plants would be absolutely insoluble, unless 
upon the entirely unscientific hypothesis of “special 
creation.” 
Geology teaches us, however—by the amplest and clearest 
evidence—that the present state of things is only the last 
phase of a long series of mutations, which began with the 
first formation of the solid crust, and which are still in 
progress. These changes are generally admitted to be the 
result of differential movements of the crust, by which 
certain areas undergo elevation or are pushed up, while 
others are depressed or sink down. The primary cause of 
these earth-movements is to be found in the slow contraction 
of the globe, consequent on the loss of its internal heat by 
radiation ; a subsidiary, but probably very active cause 
being the transference of material from one area to another, 
as the result of denudation. Roughly speaking, the elevated 
areas of the earth’s crust are the dry lands, while the 
depressed areas constitute the ocean-basins. 
Whatever differences of opinion may exist upon other 
points, there is absolute unanimity among geologists in 
believing that our existing dry lands have been repeatedly 
