Geographical Distribution of the Marine Invertehrata, 161 
Such an inquiry will best be conducted by the examina- 
tion of the marine fossils, particularly of the oldest beds. 
These forms of life are well known to have predominated 
throughout most of the geologic cycles. Indeed, only in 
the very latest epochs do terrestrial animals prevail, either 
numerically, or in geographical distribution, in anything 
like the present fashion. Now, though celebrated physicists 
have proved the amount of heat given off from the solid 
crust of the globe, in cooling down from incandescence, to 
have been so inconsiderable, even through enormous cycles 
of time such as have been hinted at, as not to affect the 
condition of organic life on the land, their calculations 
do not touch on the physical conditions that might have 
influenced marine life in geologic times. Indeed, recent 
physical data appear to assert that this variety of life might 
have been seriously affected by physical influences. Professor 
Frankland, in advancing his recent theory " on the cause 
of the phenomena of the glacial epoch," has experimentally 
shown that water cools very much more slowly than a solid 
body ; indeed, nearly twice as slowly. Now, if the tempera- 
ture of the ocean has been diminished, even in a very slight 
degree, throughout such enormous cycles of time as the cal- 
culations first referred to hint at, very decided biological 
changes must, in consequence, have occurred. An investiga- 
tion in detail, more especially of the appearance of the marine 
invertebrata, would assist us in ascertaining if such changes 
have occurred. In connection with this, the present distri- 
bution of marine animals might be carefully investigated, in 
relation to the effect of heat on oceanic life. 
In calling the attention of naturalists to this line of in- 
quiry, the author is aware that it may be shaken to its 
foundation by the investigations of another school of physi- 
cists, who deny the doctrine of the secular cooling of our 
globe altogether. Yet this apparent uncertainty as to the 
investigation ending in the elucidation of exact truth should 
not deter us from it. 
