Geographical Distribution of the Marine Invertebrata. 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. 



