92 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
a vent is once opened they do not all rush forth ‘at once, and con- 
tinue to outpour until the reservoir is completely exhausted, and 
why does not the vent thereafter close up forever? Ina word, why 
should a volcano dole out its products in driblets, instead of send- 
ing forth one stupendous belch, equal to all the driblets combined ? 
The answer here proposed is that it is because lavas, in their primi- 
tive condition, do not have sufficient potential energy, in the form 
of elastic force, to break open the covering which keeps them in; 
but they gradually acquire that energy in a portion of the reser- 
voirs at a time, and when a sufficient portion of them has acquired 
it the covering is ruptured, and the whole of this energetic portion 
is extravasated. The vent then closes, and the process is repeated 
upon a second installment. The agency which thus progressively 
develops this force is the missing factor, and when we discover it 
we shall discover the secret of the volcano. 
The third general fact to be taken account of is the enormous 
quantity of heat given off by volcanoes through long periods of 
time without any sign of exhaustion. The quantity of heat brought 
up by the lavas themselves is but a fraction of the whole amount 
dissipated. Kilauea wastes many times more heat by quiet radia- 
tion from the surfaces of its lava lakes and by steaming and by 
numberless modes of escape than by actual eruption of lavas. 
Mauna Loa also dissipates the greater part of its heat in the same 
way, and the same fact is wholly or partially true of all other active 
or intermittent volcanoes. And yet for very long periods, for thou- 
sands of centuries, these great volcanoes show no sign of heat-exhaus- 
tion; on the contrary, such indications as we have suggest the con- 
clusion that the earth beneath them is hotter than before. 
A fourth general fact is that volcanoes are located in areas which 
have recently been or are now undergoing elevation. 
All these facts suggest the action of some cause generating heat 
within the earth. This cause, if such it be, is for the present wholly 
mysterious and unknown. 
Mr. PowELL, referring to the relation between volcanic eruption 
and elevation, said that the typical, secular sequence of geologic 
events was, first, elevation, resulting in, second, degredation, accom- 
panied by, third, extravasation, followed sooner or later by, fourth, 
subsidence, resulting in, fifth, sedimentation. There are numerous 
regions in which this circle of events ha8 been recorded, and in 
some places it has been repeated two or three times. 
