THE GROWTH OF CONTINENTS. 125 
striking enough to change the general aspect of 
the organic world. This age was throughout, in 
its physical formation, the age of large continen- 
tal islands ; while in its organic character it was 
the age of Reptiles as the highest animal type, 
and of Gymnosperms and Monocotyledonous 
plants as the highest vegetable groups. 
There was an age in the physical history of the 
world when great ranges of mountains bound to- 
gether in everlasting chains the islands which 
had already grown to continental dimensions, — 
when wide tracts of land, hitherto insular in 
character, became soldered into one by the up- 
heaval of Plutonic masses which stretched across 
them all and riveted them forever with bolts of 
granite, of porphyry, and of basalt. Thus did 
the Rocky Mountains and the Andes bind to- 
gether North and South America; the Pyrenees 
united Spain to France ; the Alps, the Caucasus, 
and the Himalayas bound Europe to Asia. The • 
class of Mammalia was now at the head of the 
animal kingdom ; huge quadrupeds possessed the 
earth, and dwelt in forests characterized by plants 
of a higher order than any preceding ones, — the 
Beeches, Birches, Maples, Oaks, and Poplars of 
the Tertiaries. But though the continents had 
assumed their permanent outlines, extensive 
tracts of land still remained covered with ocean. 
Inland seas, sheets of water like the Medi terra- 
