


ORE-FORMATIONS 237 
one or other of the “irreguiar formations.” Nevertheless, the 
classification here adopted serves to bring prominently into 
view the various conditions under which the epigenetic ore- 
formations occur. 
I. FISSURE VEINS OR LODES 
Nature of Fissures.—An ore-vein or lode may be defined 
as a rent or fissure filled with metalliferous and other minerals 
alone, or with rock-débris in addition. The fissures in which 
true lodes occur are often mere chinks or wider clefts, along 
which no rock-displacement may have been effected. Narrow 
fissures of this kind may occur singly, but often quite a large 
number, occupying parallel or 
nearly parallel positions, traverse 
the rocks in some given direction. 
None of these may show slicken- 
sides or yield any evidence of Se Za 
slipping or faulting. Not infre- FOS be 
quently, however, the fissures 
SGeeupied. by lodes are faults, 
although it would seem that the 
amount of rock-displacement (when 
that can be measured) is seldom 
very great—not often exceeding 
two or three hundred feet, and 
being usually much less. Many ore- 
bearing faults, however, traverse 
highly disturbed and schistose rocks, and the amount of dis- 
placement in such cases must be quite conjectural. Be that 
as it may, it would appear that the larger dislocations occur- 
ring in a region rich in lodes are seldom ore-bearing. The 
faults occupied by lodes may be normal or reversed. Few 
lodes are quite vertical, but the great majority approach 
verticality—the inclination from the vertical being termed 
the hade or underlie. The rocks traversed by a lode are 
known as the country or country-rock ; and the wall of the 
fissure which overhangs the miner when standing upright is 
termed the Langing-wall; while that on which he stands is 
the footwall (see Fig. 86). 


FIG. 86.—FISSURE-VEIN OR 
LODE. 
