REVOLUTION VS. EVOLUTION 
317 
short interval of upheaval. The revolution was a success only 
because of the preceding preparatory development which pro- 
gressed so deliberately and inconspicuously that it entirely 
escaped the attention of the earlier students of ancient life, 
thrilled as they were by the apparantly abrupt and sweeping 
changes which the revolution wrought. Those reforms’^ 
were merely the climacteric fruition of a lengthy period of pre- 
paratory evolution. 
Examples without number, drawn from other classes of 
animal and of plant life at this same milestone in the progress 
of life, parallel this one. The same story recurs again and 
again as other milestones are passed. We may pause for but * 
one other illustration. 
The transition from the Mesozoic Era to the Cenozoic Era, 
the era of modern life, is marked by physiographic and climatic 
changes not unlike those which characterized the transition 
just sketched. Once more, the stresses slowly accumulating 
within the rigid body of the earth were piled one upon another 
until they could be no longer resisted; the pent-up energies must 
be released as before. But the chief scenes of the drama were 
staged in other places; the most conspicuous milestone is found 
where the American Cordillera rears its cloud-swept peaks from 
Alaska to Cape Horn. This mightiest of all but one of the 
modern mountain systems dates its birth from the close of the 
Age of Reptiles. The travail which brought it into existence 
was marked by violent volcanic outbursts on a gigantic scale; 
Vesuvius, Stromboli, Krakatoa, Pelee and Mauna Loa, all 
crowded into a single county and set in simultaneous eruption 
would perhaps give some idea of the events which constitute 
episode one of this second serial. Again, there was a general 
elevation of the continental platforms and a withdrawal of the 
shallow seas to the newly deepened ocean basins. Again, 
there were far-reaching climatic changes; even another glacial 
episode, if, as seems probable, the glacial deposits recently 
discovered in Colorado and British Columbia date from this 
time. Again, there was a second mountain-making crumpling 
of the earth ^s crust, this time concentrated in the same cordillera 
