54 GEOLOGICAL SURVEY 
In the Tertiary, Gastaropods abound. 
The Cetacea, such as Zeuglodon, Manatus, and other genera, are found here. But the most 
remarkable feature in the Fauna of this period is the great number of huge Pachydermatous mam- 
malians which seem to have suddenly started into existence, bearing the same relation to this 
period that the enormous reptiles did to that of the Lias and Oolite. Remains of the rattlesnake, 
opossum, horse, and monkey belong to this series, and towards its close the mammoth, mastodon, 
and megatherium make their appearance. And last of all man appears on the earth. 
In taking a general view of this sort, questions as to the origin and extinction of species force 
themselves upon the mind of the most thoughtless. Did species first come from the hand of the 
Creator in the form in which we find them, or did they pass through a series of metamorphoses, 
by which they were gradually changed and perfected? A superficial observer, in casting his eye 
over a collection of organic remains, would no doubt be struck with the evidences of progression 
that it presents. Buta thorough examination, supposing he had the patience to make it, would 
satisfy him that this progression, so far as it exists, is the result of a design, having for its object 
adaptation to external existing circumstances, and not giving the slightest countenance to any 
development by metamorphosis or transmutation. 
Some writers have attempted to account for the origin of life by supposing that animalcules were 
living atoms of elementary matter, which, by their aggregation or coalescence, produced higher 
animals. 
Akin to this theory is that of “spontaneous generation,” which is often flippantly expressed 
by the phraseology— Matter placed under favorable circumstances may produce life.” The 
experiments of Cross, who it was supposed had produced living infusoria by galvanic action, and 
existence of the intestinal and other worms where it was once found difficult to account for their 
presence, have all been adduced in proof of this theory. 
With regard to animalcules, it is now well known, from the labors of Ehrenberg and others, that 
the most minute of these little forms are well organized animals, presenting the relations of parent 
and offspring just as distinctly as they are found in higher organisms. Ehrenberg and Agassiz 
have repeatedly seen them laying eggs, and studied the form and growth of the young within 
these eggs. These facts were not known to these who first proposed the theory of “living elemen- 
tary atoms.” We have not the slightest evidence, any where, of the union of organized beings, to 
form a higher animal. Had such existed, it would have been long since discovered, if it were not 
sufficiently opposed to the whole plan exhibited in animated nature. 
“ Spontaneous generation” takes for granted what it should prove, for it supposes matter endowed 
with the attributes of life, and capable of performing one of its highest functions, before life has 
yet existed, which is sufficiently absurd. 
Cross’s experiment proves’ too much: for the animal supposed to be produced belongs to the class 
Articulata, which stands high in the scale of being, and includes forms of high organization. It 
should have commenced lower in the scale. Besides, the experiments, or rather their results, are 
far from being considered as conclusive, by those best capable of appreciating such processes. 
The worms found in the intestinal and other cavities of animals are frequently alluded to, and 
are even supposed to originate in those cavities. It is not surprising that such opinions once existed. 
when science could offer no better theory—and the uninformed are most given to theorize. 
