90 
TERTIARY DEPOSITS. 
short of the point reached by its predeces¬ 
sor. 
It will be convenient therefore to consider 
the formations in the actual order of their 
occurrence at the surface, and we may do 
this with suffieient completeness by assum¬ 
ing that our student commences his journey at 
the metropolis, and shapes his course west¬ 
ward in search of primary rocks. 
1 . Tertiary deposits. The first portion 
of his travels lie over the tertiary strata. 
This name was given to the collection of 
sands and clays which form the centre of 
France, and the subsoil of the London dis¬ 
trict, to distinguish it as the third term in the 
supposed upward process from the primitive 
to the present; it is still retained as a con¬ 
venient appellation for the groupe which has I 
since received the more significant names of 
Eocene, Miocene, and Pleiocene. 
One of the mounds arising from a street 
excavation in the metroi)olis, so obstructive 
to all save the geological passenger, may 
supply the latter with materials for beginning 
his collection of facts. 
