112 The American Naturalist. [February, 
of the Ozarkian epoch has superior claims over the opening 
-of the Kansan epoch. 
The great geological eras are demarked by widespread un- 
conformities and a radical change in sediment. As every 
effect has had a cause adequate to produce it, it may be as- 
sumed that these breaks in the sedimentary series were cor- 
related with and directly dependent upon great changes of the 
‘land areas, usually of continental and often of almost world- 
wide extent. These changes were of the nature of great earth 
pulsations, uplifting and depressing the continental plateaux, 
-and, when the contraction of the earth’s crust was very severe, 
corrugating it and even, at times, fracturing it along certain 
lines of weakness. The new geological era thus instituted is 
usually considered to date from the time that the disturbance 
first assumed prominence, modifying the flora and fauna of 
the land areas and the nature of the sediment deposited in the 
-sea about their borders. In short, it may be considered a rule 
that the natural opening event of the eras previous to the 
‘Quaternary as at present constituted, was a profound distur- 
bance of the earth’s equilibrium, and it does not seem to the 
writer that this rule should be set aside in subdividing the 
later geological history. Therefore, convenience and the need 
of a classification based strictly upon natural conditions, seem 
to demand that the Ozarkian epoch should be included under 
‘the term Quaternary era. 
If we accept the above proposed innovation on the gener- 
ally accepted scheme of geologic time divisions, we are con- 
strained to reconstruct the previously established Quaternary 
classification. For it will soon become evident that the time 
of Ozarkian high-level of the continent deserves more than 4 
mere recognition as an epoch equivalent in significance to any 
one of the succeeding glacial or interglacial epochs. It was 
pre-eminently a time of comparatively elevated conditions of 
the land without glaciation. Succeeding it was a period chat- 
acterized by alternating glacial and non-glacial conditions, 
rapid epeirogenic movements, repeated migrations of faunas 
and floras, but no long continued high-level conditions. In 
point of time the former or Ozarkian period or epoch was by 
