xviii INTRODUCTORY AND EXPLANATORY 
the Jurassic, when the Dinosaurs held carnival, . 
variously put at from 15,000,000 ta 6,000,000 
years; while from the beginning of the Eocene, 
when the mammals began to gain the suprem- 
acy, until now, the figures vary from 3,000,000 
to 5,000,000 years. So the question of age will 
be left for the reader to settle to his or her satis- 
faction. 
The restorations of extinct animals may be 
considered as giving as accurate representations 
of these creatures as it is possible to make ; they 
were either drawn by Mr. Knight, whose name 
is guarantee that they are of the highest quality, 
or by Mr. Gleeson, with the aid of Mr. Knight's 
criticism. That they are infallibly correct is out 
of the question ; for, as Dr. Woodward writes 
in the preface to “ Extinct Monsters,” “ restora- 
tions are ever lable to emendation, and the pres- 
ent . . . will certainly prove no exception 
to the rule.” As a striking instance of thas, it 
was found necessary at the last moment to 
change the figure of Hesperornis, the original 
life-like portrait proving to be incorrect in 
attitude, a fact that would have long escaped 
detection but for the Pan-American Exposition. 
