REVIEWS—A MANUAL OF GEOLOGY. 53 
which cannot be over a twentieth of all that have covered the earth in its 
former ages. 
4. The extermination of species was in general due to catastrophes, while the 
extinction of tribes or higher groups may have been a consequence of secular 
changes in the condition of the climate, atmosphere, or waters.—The extermination 
of species here alluded to, and some of the kinds of catastrophes which caused 
them, are briefly considered on p. 398. 
5. With regard to the Organization of Species, Geology suggests no theory of 
natural forces. It is right for science to search out Nature’s methods, and strive 
to employ her forces—organic or inorganic—in the effort, vain though it prove, 
to derive thence new living species. The study of fossils has given no aid in 
this direction. It has brought to light no facts sustaining a theory that derives 
species from others, either by a system of evolution, or by a system of variations 
of living individuals, and bears strongly against both hypotheses. There are no 
lineal series through creation corresponding to such methods of development. 
Instead of gradations from'Mollusks or Articulates to the lower Fishes, and so 
on upward, the Fish-type commences near its summit-level, or rather between 
the level of the typical fish and that of a higher class of Vertebrates. Wera 
either of these plans the system in nature, examples of the blending of species 
would be common through all the classes, high and low; and North America 
would afford them as successive stages between the old Elephant or Mastodon 
and earlier species, and so throughout the various tribes of life, animal and 
vegetable. But, in fact, appearances suggesting the idea of such shadings 
among species are exceedingly rare,—wonderfully so, considering that Palzon- 
tology has only the imperfect stony secretions of animals to study out, which 
Sometimes afford insufficient distinctions even when perfect and from living 
species. Under any scheme of development of species from species, the system 
of life, after ages of progress, would have become a blended mass,—the temple 
of nature fused over its surface and throughout its structure. The study of the 
past has opened to view no such result. 
Geology appears to bring us directly before the Creator; and, while opening 
to us the methods through which the forces of nature have accomplished His 
purpose,—while proving that there has been a plan glorious in its scheme and 
perfect in system, progressing through unmeasured ages and looking ever 
towards man and a spiritual end,—it leads to no other solution of the great 
problem of creation, whether of kinds of matter or of species of life, than this :— 
Devs FucIr. 
In closing this brief notice of Professor Dana’s excellent treatise, 
we may observe that the author appears to have carefully avoided, 
throughout, the adoption of any one-sided views. In all debatable 
eases, the opposite sides of the question are equaily discussed: a 
method of treatment which adds much to the value of the work. 
E. J. C. 
