GAUDRY AND EVOLUTION—GLANGEAUD. 427 
and it is to discover this plan and to explain it that he wrote these 
remarkable works and consecrated his life.” (Liard.) 
In 1896 Gaudry published another treatise as a supplement to his 
“Enchainements.” This is the “Essay on philosophical paleontol- 
ogy,” in which he revealed his thought on the problems raised by 
the study of paleontology. 
In a series of chapters he showed that animated nature formed a 
great unity, the development of which it was possible to trace as one 
traces that of the individual. He passed in review the multiplication 
of organisms, their differentiation, the growth of their bodies, the 
progress of their activities, their sensibilities, and their intelligence. 
A practical idea which proceeds from his studies is that which re- 
lates to the determination of the age of the terrestrial strata by means 
of the stage of evolution of the animals found therein. ‘ No one de- 
nies to-day that by the aid of fossils it is possible to determine the 
age of formations. It is admitted that each of them contains a cer- 
tain number of characteristic fossils. Why are they characteristic 
of one epoch rather than another? No one knew formerly, and that 
could not fail to be displeasing, because one does not enjoy what one 
does not comprehend and has great difficulty in remembering. But 
if paleontology gives us the assistance of a regular evolution of ani- 
mated nature, it is evident that the stage of development of the fos- 
sus corresponds to their geological age.. We then understand why 
certain fossils are found at a certain horizon. The stages of evolu- 
tion of the fossils which are brought to us for identification mark not 
only the modifications of organization, but also of the principal divi- 
sions of geological time. Taking two different strata, if I find that in 
one the animals indicate a condition of evolution less advanced than 
the other, I conclude that the former are of the earler age.” 
(Gaudry.) 
Thus, according to the state of development of the vertebral column, 
the tail, the teeth, or the scales on the body of fishes one can dis- 
tinguish the Primary, the middle of the Secondary, and the Tertiary. 
Reptiles with the vertebral column imperfectly ossified indicate the 
Primary. The apogee of the reign of the reptiles announces the 
Secondary. Their resemblance to types now living indicates the 
Tertiary. 
If one show to a paleontologist feet or teeth of various animals 
of different epochs, he will often say, “ this is the foot of an Eocene, 
Oligocene, or Miocene animal,” etc. Some modifications apart, the 
history of the discoveries of recent years, those relating to the Pro- 
boscidians, for example, offers a striking confirmation of these ideas, 
which are only a direct corollary of the continuous evolution of 
organisms. 
