THE OZARKIAN AND ITS SIGNIFICANCE S41 
we may have examples of both old and new topography. But 
in any case a critical period, being the beginning of a new great 
cycle, after such a period we have only or mainly new topogra- 
phy. This is the true and conclusive answer to Professor Tarr’s 
objection to Professor Davis’ far-reaching deductions from the 
supposed discovery of the remnants of former peneplains. 
Professor Tarr objects that if there be any such former pene- 
plains there ought to be peneplains formed now and in the pres- 
ent geological epoch—that the very foundation of geology as 
an inductive science consists in the use of causes and processes 
now in operation as the basis of reasoning on phenomena of 
earlier times. Yes, causes and processes now in operation, but not 
results and forms now existent and produced in the present 
epoch. Causes and processes are constant, or nearly so, but 
resulting forms pass through a regular cycle of evolution- 
changes. Now the dast cycle 1s just commenced. We must wait 
at least a few millions of years before we can expect to find 
peneplains made out of the recently inaugurated and highly 
emphasized topographic forms. Asa note of warning against 
hasty generalizations Professor Tarr’s paper cannot be too 
highly commended. We are all too apt to be carried away by 
a new idea. It is apt to become a fashion of thought for which 
we are ever seeking confirmation ; and in all complex and imper- 
fectly understood questions, what we seek earnestly for we are 
very apt to find. It is possible, yea, it is probable, that the pene- 
plain idea has been overworked; that many of these ancient 
peneplains exist only in the fervid imagination of the too ardent 
seologist, Nevertheless, the: principle is a true one and 
undoubtedly a very fertile one. Geological history has hereto- 
fore been based almost wholly on the results of sedimentation. 
It is time that it should be based also, and equally, on the 
results of erosion. These results may be more difficult of inter- 
pretation, but difficulties ought only to stimulate investigation. 
Is the Ozarkian Tertiary or Quaternary? Finally, we are now 
prepared to return to the question of place of Ozarkian in the 
geological classification. After what has been said the answer 
