This period, one of the most important in the physical history of the
globe, has received its name from the Jura mountains in France, the Jura
range being composed of the rocks deposited in the seas of the period.
In the term Jurassic, the formations designated as the “Oolite” and
“Lias” are included, both being found in the Jura mountains. The
Jurassic period presents a very striking assemblage of characteristics,
both in its vegetation and in the animal remains which belong to it;
many genera of animals existing in the preceding age have disappeared,
new genera have replaced them, comprising a very specially organised
group, containing not less than 4,000 species.
The Jurassic period is sub-divided into two sub-periods: those of the
_Lias_ and the _Oolite_.