THE OZARKIAN AND ITS SIGNIFICANCE 537 
slow at first, but rapidly increasing toward the end and culmina- 
ting in the formation of the Appalachian chain. Concurrently 
with this there was, almost certainly, a gradual decrease of tem- 
perature rapidly culminating at the end in something approach- 
ing, at least, a true glacial epoch in the Permian. Similarly, 
there was probably, during the Tertiary, a gradual elevation and 
increase of land and diminution of temperature, culminating 
somewhat rapidly at its end, in the Ozarkian elevation and the 
Glacial ice sheet. Similar changes occurred at other critical 
periods, but less conspicuously. 
I have been accustomed, in default of any other and more prob- 
able cause, to attribute the increase of cold directly to the increase 
of elevation, although admitting its possible insufficiency. It is 
this apparent insufficiency that constitutes the only justification 
of extra-terrestrial theories of Glacial climate, such as Croll’s, 
etc. Recently Professor Chamberlin has contributed to the Jour- 
NAL OF GEOLOGY* some admirable and suggestive speculations on 
the cause of these cycles of climate and of life. According to him, 
the continental elevation is not the direct, but mainly the zudz- 
vect cause of cold, by the exhaustion of the supply of CO, in 
the air by continuous rock-decay during these land-periods. 
This supply is supposed to be restored from the interior of the 
earth through fissures, etc., produced by the commotions of these 
times. He, moreover, correlates these changes in elevation and 
in temperature in a most suggestive way with alternating richness 
and poverty of life and corresponding alternations of limestones 
and sandstones. I cannot, of course, dwell on these very sug- 
gestive views, but only draw attention to the fact that the cycles 
of which Professor Chamberlin speaks correspond to the smaller or 
subordinate cycles spoken of on pages 536 and 537, and of to the 
great cycles separated by critical periods and constituting eras. 
Nevertheless, there is no reason why similar causes acting with 
greater intensity at long intervals should not determine the 
greater cycles also. 
3. Cycles of geographic diversity of organic forms and of rates of 
*JouR. GEOL., Vol. VI, pp. 597, 609, 1898. 
