80 TERTIARY SERIES. 
genera of the higher orders of animals, which 
seem to have been constructed with a view 
to the temporary occupation of the earth, 
whilst the tertiary strata were in process of 
formation. Our globe was no longer tenanted 
by those gigantic reptiles, which had been its 
occupants during the secondary period ; neither 
was it yet fit to receive the numerous tribes of 
terrestrial mammalia that are its actual inhabi- 
tants. A large proportion of the lands which 
had been raised above the sea, being covered 
with fresh water, was best adapted for the abode 
of fluviatile and lacustrine quadrupeds. 
Our knowledge of these quadrupeds is derived 
solely from their fossil remains ; and as these 
are found chiefly (but not exclusively)^ in the 
fresh-water formations of the tertiary series, it is 
to them principally that our present attention 
will be directed. 
* The remains of Paloeotherium occur, though very rarely, in 
the Calcaire Grossier of Paris. The bones of other terrestrial 
mammalia, occur occasionally in the Miocene and Pliocene marine 
formations, e. g\ in Touraine and in the Sub-apennines. These 
are derived from carcases which, during these respective periods, 
were drifted into estuaries and seas. 
No remains of mammalia have yet been found in the Plastic 
clay formation next above the chalk ; the admixture of fresh- 
water and marine shells in this formation seems to indicate that it 
was deposited in an estuary. Beds of fresh-water shells are in- 
terposed more than once between the marine strata of the Cal- 
caire Grossier, which are placed next above the plastic clay. 
