INTRODUCTION. 
XXI 
the aquatic species, would have been poisoned by it; they could only 
appear after the atmosphere had been purified by plants absorbing 
the carbon and giving off oxygen. At the earliest assignable period 
of creation the vegetable kingdom showed the greatest uniformity, 
while, on the contrary, the animal world showed some variety. 
In the grauwacke we already find flower-like, radiate, soft-bodied, 
and crab-like creatures, and, rarely, fish, which, as aquatic animals, 
may possibly have been the first representatives of the vertebrates. 
In the coal measures the above classes subdivide themselves into 
genera and species. The first terrestrial vertebrate animal, a lizard, 
is found in the Zechstein, or magnesian limestone, group of Permian 
(Upper Paleozoic age). From this new forms are continually appear¬ 
ing, until we find on the Upper Jura the bone remains of birds and 
mammals; even the feathers and eggs of these early forms of birds 
have come down to us. The Cannstadt calcareous-tufa has stored up 
for us the most exquisitely preserved eggs and feathers of primaeval 
birds. In the Island of Madagascar giant specimens of petrified eggs 
have been dug up, belonging to birds of which we can scarcely form 
any idea. 
Although we have now, in a certain degree, determined the period 
at which birds first existed, we have, notwithstanding all our expe¬ 
rience, not obtained any satisfactory explanation of the words:— 
“ Let there be.and it was so.” Creation, as much as Life itself, yet 
remains a mystery. Still it need not appear to us more wonderful 
than the origin of an animal existing at this moment, of whose 
development we have evidence before our eyes at the present day. 
We may well call the one “natural,” and the other “wonderful ,”—“For 
all the workings of Nature are wonderful, and all her wonders natural .” 
Many have essayed to explain this text. Some argue the origin of 
birds to have arisen from primaeval eggs, inasmuch as they would fain 
interpret the secrets of the past by what is obvious in the present. 
They have comprehended the wonder not one whit better than those 
who would see a full-fledged and perfect bird arise from the early 
slime, like the Grecian Aphrodite from the foam ! The first of these 
would do away with the perfect plant, and confine themselves simply 
to the germ, as though it were less wonderful than the tree which 
springs from it! 
We must, however, quietly admit that this war of words leads to 
the brink of a gulf which we are at present utterly unable to span. 
