It has not been my object to present in the following pages even an
approximately complete description of the volcanic and seismic phenomena
of the globe; such an undertaking would involve an amount of labour
which few would be bold enough to attempt; nor would it be compatible
with the aims of the _Contemporary Science Series_.

I have rather chosen to illustrate the most recent conclusions regarding
the phenomena and origin of volcanic action, by the selection of
examples drawn from the districts where these phenomena have been most
carefully observed and recorded under the light of modern geological
science. I have also endeavoured to show, by illustrations carried back
into later geological epochs, how the volcanic phenomena of the present
day do not differ in kind, though they may in degree, from those of the
past history of our globe. For not only do the modes of eruption of
volcanic materials in past geological times resemble those of the
present or human epoch, but the materials themselves are so similar in
character that it is only in consequence of alterations in structure or
composition which the original materials have undergone, since their
extrusion, that any important distinctions can be recognised between the
volcanic products of recent times and those of earlier periods.

I have, finally, endeavoured to find an answer to two interesting and
important questions: (1) Are we now living in an epoch of extraordinary
volcanic energy?--a question which such terrible outbursts as we have
recently witnessed in Japan, the Malay Archipelago, and even in Italy,
naturally suggest; and (2) What is the ultimate cause of volcanic
action? On this latter point I am gratified to find that my conclusions
are in accordance with those expounded by one who has been appropriately
designated "the Nestor of Modern Geology," Professor Prestwich.

Within the last few years the study of the structure and composition of
volcanic rocks, by means of the microscope brought to bear on their
translucent sections, has added wonderfully to our knowledge of such
rocks, and has become a special branch of petrological investigation.
Commenced by Sorby, and carried on by Allport, Zirkel, Rosenbusch, Von
Lasaulx, Teall, and many more enthusiastic students, it has thrown a
flood of light upon our knowledge of the mutual relations of the
component minerals of igneous masses, the alteration these minerals have
undergone in some cases, and the