562 LT. 6 CHAMBERETN, 
It is of supreme importance therefore to consider irregularities 
in the action of the sources of loss and gain. 
Varying rates of gain—The constancy or irregularity of the 
sun’s contribution—assuming it to make a recognizable contri- 
bution—is quite unknown. It would presumably be dependent 
upon the internal explosive action of the sun concerning which 
all thought is as yet highly speculative. So far as its relations to 
geological periods are concerned, it would probably be either an 
essentially constant factor or one which would not fall in syste- 
matically with any special phase of geological progress, and 
could not be regarded as a codperative factor in any definite 
phase. It might be progressively increasing, as the sun concen- 
trates, or progressively diminishing. 
Much the same is to be said with regard to possible sources 
of supply from meteoric and similar extra-terrestrial sources. 
The extrusion of gases and vapors from the interior has been 
presumably periodic, because the conditions of molten eruption 
and of mechanical disruption have probably been periodic rather 
than constant. No specific determination of the periodicity of 
volcanic action has yet been made out, but the testimony of 
present geological data is to the effect that vulcanism has been 
more frequent and intense at certain periods than at others. 
This is clearly true for individual grand divisions of the earth, 
and seems to be true of the earth at large, notwithstanding the 
fact that vulcanism was a more or less local phenomenon. While 
a definite periodicity, specifically connected with other phe- 
nomena, cannot now be affirmed, the tentative proposition that 
vulcanism has been more abundant in great periods of readjust- 
ment than in periods of quiescence may be entertained. The 
connection with those periods seems sometimes to have been 
very intimate and immediate, and at other times more remote. 
So far as disruption of the rocks constitutes a means of escape 
for internal gases, there should obviously be a close connection 
with periods of readjustment. In a rather general and uncertain 
way, then, it would seem necessary to assume, in a working 
hypothesis, that the enrichment of the atmosphere from internal 
