

CHAPTER AX 
ECONOMIC ASPECTS OF GEOLOGICAL STRUCTURE 
The Search for Coal—Conditions under which Coal occurs. Trial 
Borings. The Search for Ores— General Considerations which 
should guide the Prospector ; Nature of the Evidence. Geological 
Structure and Engineering Operations — Excavations, Tunnels, 
Foundations. 
IN preceding chapters dealing with Tectonic or Structural 
Geology, much that is of interest and importance to engineers 
and others has been set forth in more or less detail. No 
attempt, however, has been made to indicate the various 
ways in which a knowledge of rock-structures may be utilised 
by mining and civil engineers, architects, and others—for 
the simple reason that the application of the knowledge in 
question must be sufficiently evident. In the present chapter, 
however, it may not be out of place to give a few supple- 
mentary notes which could not be well inserted in earlier 
pages. 
The Search for Coal.—In regions the geological structure 
of which is well known, and good maps of which are available, 
not much difficulty need be experienced by the mining 
engineer who can read and interpret geological maps and 
sections. He may often be at a loss, however, in searching 
for coal, etc, in a country the geology of which is only 
imperfectly understood, or even not known. Under such 
conditions his first care would necessarily be to ascertain 
the geological age of the sedimentary strata by searching 
for fossils. Coal occurs in several geological systems. In 
Britain, workable seams are practically confined to the 
Carboniferous system, and the same is largely the case in 
many other regions, both in Europe and North America, 
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