19 
There is sufficient ground in the above facts to believe that, in certain 
parts at least of the ocean, there must exist some agency by which the 
waters of the lower strata acquire greater warmth than could have been 
anticipated, and certainly there is no evidence to show that they ever lose 
their fluidity, or cease to continue a medium in which organic life may 
continue. If there be truth in the theory of the earth’s central heat, it 
may be that the temperature of the lowest depths of the ocean, depths 
measurable by miles rather than fathoms, may equal or even exceed that 
of the surface. 
When we remember how highly stimulant of increase of size heat is in 
most divisions of the animal kingdom, it is not inconsistent with analogy 
to imagine, that in those parts where the energies peculiar to the marine 
creation exist in largest force and area, there also will be the greatest deve^ 
lopment of form. We see the oceanic fishes and even those of deep lakes 
greatly exceeding in size the denizens of the shallow waters, and geologists 
universally ascribe the giant proportions of the reptiles of former periods 
to the high temperature then prevailing on the globe.* It will be in place 
here to enumerate some of the largest creatures both of past and present 
existence; and to afford a ready standard of comparison, we will commence 
by naming the great rorqual, black whale, or finner. (See Plate No. 1.) 
This is probably the hugest of living creatures, attaining a length of 120 
feet, with a circumference of 30 to 40 feet; being in bulk the counterpart of 
a vessel of 300 to 400 tons burthen. Dead specimens have been measured 
105 feet in length. The basking shark attains 40 feet, and from the 
fossil teeth of the white shark occasionally found, it is supposed formerly 
to have reached a length of 60 feet. The extinct saurians, if extinct they 
he , such as the ichthyosaurus and plesiosaurus attained 20 to 25 feet in the 
* It is not intended to press this argument to its full extent, or to insinuate that the 
higher the temperature, consistent with life, the larger will be the development of 
animal organization, for this is not borne out by facts either past or present, especially 
with regard to fishes. 
If we refer to the fossils of the distinct geological periods, it is only in the later for¬ 
mations that we find the gigantic remains of the former denizens of the waters, while in 
the earlier fossiliferous rocks, not only, we believe, are no reptiles discovered, but the same 
races of fish, sharks for instance, which subsequently expand so enormously, are seen 
of most diminutive size, measurable by inches instead of yards. The undue presence 
of carbonic gas in the atmosphere, however favourable for the growth of marine and 
aqueous vegetation, may account for the non-existence of terrestrial animals in those 
earlier periods; but this cause would not, we imagine, have anything to do with fishes, 
the inhabitants of another medium; their undeveloped size, therefore, must rather be 
referred to the too high temperature of the waters. It is probable that the degree of 
heat most favourable for expansion of size among fishes, may be fixed at a lower range 
than that for reptiles, or even terrestrial animals generally. 
