PRELIMINARY REMARKS. 
5 
lizards of the present. It is a favorite inference with a certain 
class of the progressive geologists, that the oxygen of the 
atmosphere at that period was less in proportion to its mass 
than it is now. But then may we not inquire, if there was less 
oxygen in the present atmosphere than there actually is, could 
the membranous reptile lung supply the demands of the system; 
and is not the constituent proportion of oxygen the quantity 
required to give the creature the power to breathe at all? I 
say it is not always safe to reason from structural affinity to 
physical conditions. If we take any other organ, as the eye, 
and draw from its structure and condition analogous inferences 
concerning the quantity of light, we may see where it will lead 
us. A class of progressive geologists, maintaining that in the 
early periods of life the light of the globe was dim. and that 
but few rays shone through the hazy atmosphere, find in sup¬ 
port of this doctrine the fossil remains of a fish or a lizard 
with enormous eye sockets. He believes that the large eye 
was adapted to a dim state of the atmosphere. Another person 
ffnds a fossil with very small bony sockets. In this case, too, 
it may be said the eye was very small, and hence it was adapted 
to an exceeding intense light—-to the sun when it shone fiercely 
from its throne in the heavens. But again, a fossil is found 
entirely destitute of an eye socket, and not a vestige of an organ 
of vision can be found; hence there was a time when the earth 
was shrouded in darkness, for in darkness animals have no need 
of eyes, and light would be useless to animals destitute of the 
visual organ. But then we find all these states of the eye in 
the present arrangements for supplying the world with light. 
The Pomatomus telescopium, a fish of the Mediterranean, 
which lives in very deep water, has a remarkably large eye.. 
It is the position which it occupies that requires the large eye, 
and that large eye is adapted to its abode; and if only one-half 
of the light of the sun was extinguished, it probably would be 
unable to see at all. And just so with the reptile, if one-half 
of the oxygen of the atmosphere was withdrawn from it, all 
reptiles would die. The mole has a very small eye, but that 
