I24 EVOLUTION..OF LIFE. 
same time. The earth has, no doubt, from time to time 
experienced great changes, its life being more or less 
destroyed by the effects of earthquakes, volcanoes, etc, 
These catastrophes were, however, local in their effects, 
as at the present day. If living plants and animals be 
compared with those whose remains have been preserved 
in the rocks, we see that, while many species and genera 
have passed away, comparatively few orders have become 
extinct, — that is, there are very few fossils which have 
not their modern representatives. Further, where the 
rocks overlie or follow each other, plants and animals 
appear in the later formation which did not pre-exist in 
the earlier, and usually exhibit a more complex structure. 
So that the “persistent types of life" seem to have been 
more or less modified from time to time. These general 
conclusions are in perfect harmony with the doctrine of 
the gradual development of the higher forms of life from 
the lower. We turn now to Embryology, which confirms, 
in the most remarkable way, the tree of life deduced from 
the structure and fossil remains of the animal and vegetal 
kingdoms. 
CLASSIFICATION OF ROCKS ACCORDING TO THEIR ORGANIC 
REMAINS. 
TIME. PERIOD. AGE. 
Silurian. 4 Mollusca, Algze. 
Primary. | Devonian. 4 Fishes, 
Carboniferous. 4 Batrachia, Acrogens. 
Triassic. 
Secondary. تھا‎ | Reptiles, Cycade. 
Cretaceous 
Eocene 
Tertiary. | Mioceno Jumat, Palms, Exogens. 
. Pliocene. 
| 
Quaternary. 1 Modern. 
