584 Ne (Op (Gla lAAH eT DIRT EIUN 
In periods of sea extension and of land reduction (base-level 
periods in particular), the habitat of shallow water lime-secret- 
ing life is concurrently extended, giving to the agencies that set 
carbon dioxide free accelerated activity, which is further aided 
by the consequent rising temperature which reduces the absorp- 
tive power of the ocean and increases dissociation. At the same 
time, the area of the land being diminished, a low consumption 
of carbon dioxide both in original decomposition of the silicates 
and in the solution of the limestones and dolomites obtains. 
Thus the reciprocating agencies again conjoin, but now to 
increase the carbon dioxide of the air. 
These are the great and essential factors. They are modi- 
fied by several subordinate agencies already mentioned, but the 
quantitative effect of these is thought to be quite insufficient to 
prevent very notable fluctuations in the atmospheric constitu- 
tion. As a result, it is postulated that geological history has 
been accentuated by an alternation of climatic episodes embrac- 
ing, on the one hand, periods of mild, equable, moist climate 
nearly uniform for the whole globe; and on the other, periods 
when there were extremes of aridity and precipitation, and of 
heat and cold; these last denoted by deposits of salt and gyp- 
sum, of subaérial conglomerates, of red sandstones and shales, 
of arkose deposits, and occasionally by glaciation in low lati- 
tudes. 
T. C. CHAMBERLIN. 
[ The continuation of this article in the next number will embrace a discussion of 
thé application of the hypothesis to known glacial periods, and to the oscillations from 
glacial to interglacial epochs, together with the agencies of localization, and a sug- 
gestion regarding the superposed minor oscillations. | 
