678 Le Cx (CLLANEBIER LTV: 
zone of effective penetration of aerated water below this is also 
deepened. Hence the alteration of the rocks is promoted. In 
stages of low elevation — stages of baseleveling, for example — 
the zone of atmospheric penetration is shallow and rock altera- 
tion proceeds slowly. From this may be deduced the law that 
during stages of depression or baseleveling, depletion pro- 
ceeded slowly. The aggregate surface must, of course, be con- 
sidered. 
To apply this law, let us assume for the moment, a uniform 
supply equal to the average rate of exhaustion. With the inau- 
guration of any great epoch of general uplift there would begin 
an era of relatively rapid atmospheric exhaustion, which would 
proceed continuously during such elevated stage and might result 
in notable atmospheric impoverishment, as the computations cited 
early in this paper show. As the cutting down of the surface 
approached baselevel, the depletion would be retarded and, the 
supply continuing the same by hypothesis, the rate of exhaus- 
tion would fall below that of supply and an epoch of enrichment 
begin. A second elevation would re-inaugurate the depletion, 
and so oscillations of enrichment and impoverishment would fol- 
low the general oscillations of the land surface.t. Applying this 
law by itself, atmospheric poverty should follow at some distance 
the stages of general elevation, and, on the other hand, atmos- 
pheric enrichment should follow at some distance the stages of 
baseleveling or depression. 
But the assumption of a uniform average supply needs revi- 
sion. In the main the igneous extrusions and crustal disrup- 
tions that are presumed to favor gaseous emanation probably 
fell in with the initiation of the elevated stages that favored 
depletion. Ina general way the curves of supply and of deple- 
tion ran together in geological history and gave a measurably 
‘More strictly, the oscillations of that part of the land surface whose rocks con- 
sumed the atmosphere by their alteration — in general terms, the crystalline areas. 
Periodic general elevations followed by general baselevelings or some notable 
approach to baselevelings, are here assumed. It would be obligatory to state the 
grounds for this in an ampler discussion, but the all too narrow limits of this paper 
make this impracticable. 
