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 agricul- 
tural 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 better- 
known 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