Parr IV.] CAINOZOIC OR TERTIARY. 837 
approaching more and more to that of the existing Mediterranean 
basin, while the majority of their fossils belong to living species. 
The Tertiary periods witnessed the development of the present 
distribution of land and sea and the upheaval of most of the great 
mountain chains of the globe. Some of the most colossal disturb- 
_ ances of the terrestrial crust of which any record remains took place 
during these periods. Not only was the floor of the Cretaceous sea 
upraised into low lands, with lagoons, estuaries, and lakes, but 
throughout the heart of the Old World, from the Pyrenees to Japan, 
the bed of the early Tertiary or nummulitic sea was upheaved into 
a succession of giant mountains, some portions of that sea-floor now 
standing at a height of at least 16,500 feet above the sea. The rocks 
deposited during these periods are distinguished from those of earlier 
times by increasingly local characters. The nummaulitic limestone 
of the older Tertiary groups is indeed the only wide-spread massive 
formation which in the uniformity of its lithological and paleonto- 
logical characters rivals the rocks of Mesozoic and Paleozoic time. 
As a rule Tertiary deposits are loose and incoherent, and present 
such local variations, alike in their mineral composition and organic 
contents, as to show that they were mainly accumulated in detached 
basins of comparatively limited extent and in seas so shallow as to 
be apt from time to time to be filled up or elevated and to become 
in consequence brackish or even fresh. These local characters are 
increasingly developed in proportion to the recentness of the deposits. 
’ The climate of the Tertiary periods underwent in the northern . 
hemisphere a remarkable change. At the beginning it was of a 
tropical and subtropical character, even in the centre of Europe 
and North America. It then gradually became more temperate, 
but flowering plants and shrubs continued to live even far within 
the Arctic circle, where, then as now, there must have been six 
sunless months every year. Growing sti]l milder the climate passed 
eventually into a phase of extreme cold, when snow and ice extended 
from the Arctic regions into the centre of Hurope and North America. 
Since that time the cold has again diminished until the present 
thermal distribution has been reached. 
With such changes of geography and of climate, the life of 
Tertiary time, as might have been anticipated, is found to have 
been remarkably varied. In entering upon the Tertiary series of 
formations, we find ourselves upon the threshold of the modern 
type of life. The ages of lycopods, ferns, cycads, and yew-like 
conifers have passed away, and that of the dicotyledonous angio- 
sperms—the hard-wood trees and evergreens of to-day—now succeeds 
them, but not by any sudden extinction and re-creation; for, as we 
have seen (p. 808), some of these trees had already begun to make 
their appearance even in Cretaceous times. The hippurites, inoce- 
rami, ammonites, belemnites, baculites, turrilites, scaphites, and other 
molluscs, which had played so large a part in the molluscan life of the 
‘ Hornes, Jahrb. Geol. Reichsanst. 1864, p. 510. 
