the Yellowstone valley burst into action after four years of rest.
The movement of the earth-wave was in general north and south, deflected
to east and west, and the snake-like fashion in which rails on the
railroad were bent indicated both a vertical and a lateral force.

This earthquake has been attributed to various causes, but geological
experts think that it was due to a slip in the crust along the
Appalachian Mountain chain. There is a line of weakness along the
eastern slope of this chain, characterized by fissures and faults, and
it was thought that a strain had been gradually brought to bear upon
this through the removal of earth from the land by rains and rivers and
its deposition in thick strata on the sea-bottom. It is supposed that
this variation in weight in time caused a yielding of the strata and a
slip seaward of the great coastal plain. Professor Mendenhall, however,
thinks it was due to a readjustment of the earth's crust to its
gradually sinking nucleus.

CHAPTER XVIII.

The Volcano and the Earthquake, Earth's Demons of Destruction.

To most of us, dwellers upon the face of the earth, this terrestrial
sphere is quite a comfortable place of residence. The forces of Nature
everywhere and at all times surround us, forces capable, if loosened
from their bonds, of bringing death and destruction to man and the work
of his hands. But usually they are mild and beneficent in their action,
not agents of destruction and lords of elemental misrule. The air,
without whose presence we could not survive a minute, is usually a
pleasant companion, now resting about us in soft calm, now passing by in
mild breezes. The alternation of summer and winter is to us generally an
agreeable relief from the monotony of a uniform climate. The variation
from sunlight to cloud, from dry weather to rainfall, is equally viewed
as a pleasant escape from the weariness of too great fixity of natural
conditions. The change from day to night, from hours of activity to
hours of slumber, are other agreeable variations in the events of our
daily life. In short, a great pendulum seems to be swinging above us,
held in Nature's kindly hand, and adapting its movements to our best
good and highest enjoyment.

But has Nature,--if we are justified in personifying the laws and forces
of the universe,--has mother Nature really our pleasure and benefit in
mind, or does she merely suffer us to enjoy life like so many summer
insects, until s