PREFACE

HE different sections of Economic Geology are
intimately connected. Thus some ore deposits
are dependent on deep-seated solutions and others
On coastal action, the characteristics of soils illustrate
tock decay and the circulation of underground water,
tarthquakes connect superficial and plutonic action as
they arise from faulting at the depth of hundreds of
miles, and the problems of water supply show that the
surface is nourished by new material from the interior.
Hence it is convenient to consider together the various
branches of civil and mining engineering and of agricultural
 geology. To cover so varied a field in a short book
renders necessary omission of reference to some metals
that throw no special light on general principles, and to
Some agencies and processes that are adequately dealt
with in geological text-books. The examples chosen
illustrate various principles and processes, the selection
being often determined by my having had the privilege
of examining them personally.
The literature of the Economic Geology is now so
overwhelming, that reference to it has had to be sternly
limited, or it would have taken an undue share of the
Space; no reference has been given to much of the betterknown
 literature, the references given being to those that
would be useful to students, or to the authorities for
evidence relied on in the conclusions adopted,
I may refer here to a few convenient sources of infor.
mation, such as the monographs on useful minerals and
ores by the Imperial Institute, to the statistics in the
annual volumes of Mineral Industry ; for the original
literature on the ores of North America, which are often
mentioned in the text, to W. Lindgren’s Mineral