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336 STRUCTURAL AND FIELD GEOLOGY 
appearances presented by them at the surface, such as the 
coloration of soils and subsoils, the character of the gossans, 
etc.,a prospector could hardly fail of success so long as his 
researches were confined within the same geological area. 
Should the same observer, however, essay to prospect in a 
totally different region, he might often be nonplussed. In 
point of fact, many mining men have wasted time and 
substance in exploring wide tracts of country which a 
knowledge of geology might have led them to avoid, as 
probably barren ground; while, on the other hand, such 
knowledge might have directed their attention to areas in 
which prospecting was likely to lead to successful results. 
Lodes and irregular ore-formations may occur in almost 
any kind of rock, and are not restricted to a particular 
geological horizon, for they are met with in Paleozoic, 
Mesozoic, and Cainozoic rocks alike. But although this is 
true, yet by far the larger number of such formations are 
associated with the older geological systems. It is exceptional 
to meet with valuable lodes, etc., in Cainozoic and even in 
Mesozoic rocks, except in the vicinity of eruptive masses. 
Most lodes, etc., are of more or less deep-seated origin, and 
are thus least likely to be met with traversing rocks of 
relatively late geological age. They are, therefore, to be 
sought for in the more ancient rocks, because these have 
experienced vast denudation, their present surface in many 
cases being several thousand feet or yards below that which 
existed at the time the lodes were being filled. It must not 
be supposed, however, that every region of highly denuded 
ancient rocks is likely to contain valuable ore-formations. 
We know, in fact, that such is not the case; but certainly it is 
to such regions that the prospector ought to turn his attention. 
The more highly folded, fractured, and dislocated the rocks 
are, the better from his point of view, while the presence of 
batholiths, sills, and dykes of eruptive rock would be rather a 
hopeful sign, as will be gathered from what has been set forth 
in Chapters XVI. and XVII. as to the mode of occurrence 
and origin of ore-formations. 
Let us suppose, therefore, that an explorer has entered a 
sorely denuded hilly or mountainous region of ancient rocks— 
the general character and geological structure of which seem 

