s from
the shore of the continent, which appears to be the seat of
exceedingly violent shocks. A similar field occurs in the Atlantic
between the Lesser Antilles and the Spanish peninsula, but no great
waves have come thence since the time of the Lisbon earthquake. The
basin of the Caribbean and the region about Java appear to be also
fields where these disturbances may be expected, though in each but
one wave of this nature has been recorded. Therefore we may regard
these secondary results of a submarine earthquake as seldom phenomena.

DURATION OF GEOLOGICAL TIME.

Although it is beyond the power of man to conceive any such lapses of
time as have taken place in the history of this earth, it is
interesting, and in certain ways profitable, to determine as near as
possible in the measure of years the duration of the events which are
recorded in the rocks. Some astronomers, basing their conclusions on
the heat-containing power of matter, and on the rate at which energy
in this form flows from the sun, have come to the conclusion that our
planet could not have been in independent existence for more than
about twenty million years. The geologist, however, resting his
conclusions on the records which are the subject of his inquiry, comes
on many different lines to an opinion which traverses that entertained
by some distinguished astronomers. The ways in which the student of
the earth arrives at this opinion will now be set forth.

By noting the amount of sediment carried forth to the sea by the
rivers, the geologist finds that the lands of the earth--those, at
least, which are protected by their natural envelopes of
vegetation--are wearing down at a rate which pretty certainly does
not exceed one foot in about five thousand years, or two hundred feet
in a million years. Discovering at many places on the earth's surface
deposits which originally had a thickness of five thousand feet or
more, which have been worn down to the depths of thousands of feet in
a single rather brief section of geological time, the student readily
finds himself prepared to claim that a period of from five to ten
million years has often been required for the accomplishment of but a
very small part of the changes which he knows to have occurred on this
earth.

As the geologist follows down through the sections of the stratified
rocks, and from the remains of strata determines the erosion which has
borne away the greater part of