VOLCANIC ACTION. 
117 
worthy of notice; while in other cases the visible activity is 
much less, but is accompanied with disastrous and terrific effects. 
A fact should be stated in this place, which is probably the 
most important one which attends volcanic activity—it is the 
change of level which a country often suffers during its parox¬ 
ismal throes. The coast of Chili, for example, in 1822, was 
permanently elevated for one hundred miles, in some places more 
than ten feet, in others less. Large areas in all countries furnish 
many facts in proof that they have undergone a similar change 
of level. It is not determinable now whether those changes 
occurred during a single paroxysmal effort; but where a coast 
has been stationary a long time, and then appears to have been 
stationary again at a higher level, the probability favors the 
paroxysmal view. But wide areas are elevated slowly, and 
apparently uniformly. Where the change is going on slowly, 
as in Scandinavia, and perhaps on our own coast, it may be 
due to the expansion of rocks by heat. 
CAUSES OF VOLCANIC ACTION. 
§ 84. Much has been said and written of the cause or causes 
of volcanic action, and for the solution of the question many 
ingenious and indeed philosophical reasons have been proposed. 
Among the causes assigned, chemical action, excited by electro¬ 
magnetic arrangements, has had many advocates. Known 
analogies are favorable to this theory. We may arrange our 
apparatus, or we may devise in the laboratory the needful con¬ 
ditions for imitating nature’s processes within the earth, hence 
its favorable reception; and it is not strange that chemical 
forces have been regarded as the prime agencies of volcanic 
action. When we take, however, a larger view of the facts 
and phenomena which constitute in the aggregate the volcanic 
forces, we can hardly refuse to admit that the chemical actions 
which no doubt go on on a magnificent scale during the erup¬ 
tive periods, are effects and not causes. We are therefore 
driven to the necessity of going still farther back in order to 
