place
at some points and down-sinking at others, it seems not unlikely that
these irregular swayings are of very common occurrence. Moreover,
astronomers are beginning to remark the fact that their observatories
appear not to remain permanently in the same position--that is, they
do not have exactly the same latitude and longitude. Certain of these
changes have recently been explained by the discovery of a new and
hitherto unnoted movement of the polar axis. It is not improbable,
however, that the irregular swaying of the earth's crust, due to the
folding of strata and to the alterations in the volume of rocks which
are continually going on, may have some share in bringing about these
dislocations.

Measured by the destruction which was wrought to the interests of man,
earthquakes deserve to be reckoned among the direst calamities of
Nature. Since the dawn of history the records show us that the
destruction of life which is to be attributed to them is to be counted
by the millions. A catalogue of the loss of life in the accidents of
this description which have occurred during the Christian era has led
the writer to suppose that probably over two million persons have
perished from these shocks in the last nineteen centuries.
Nevertheless, as compared with other agents of destruction, such as
preventable disease, war, or famine, the loss which has been inflicted
by earth movements is really trifling, and almost all of it is due to
an obstinate carelessness in the construction of buildings without
reference to the risks which are known to exist in earthquake-ridden
countries.

Although all our exact knowledge concerning the distribution of
earthquakes is limited to the imperfect records of two or three
thousand years, it is commonly possible to measure in a general way
the liability to such accidents which may exist in any country by a
careful study of the details of its topography. In almost every large
area the process of erosion naturally leaves quantities of rock,
either in the form of detached columns or as detrital accumulations
deposited on steep slopes. These features are of relatively slow
formation, and it is often possible to determine that they have been
in their positions for a time which is to be measured by thousands of
years. Thus, on inspecting a country such as North America, where the
historic records cover but a brief time, we may on inquiry determine
which portions of its area have long been exempt