612 
ELEMENTS OF GEOLOGY. 
Fig. 633. 
the points 1, 2, 3, 4, 5, we obtain an irregular aperture at c, and 
isolated cavities d d and when we compare such figures 
with nature we find that, with certain modifications, they 
represent the interior of faults and mineral veins. If, in¬ 
stead of sliding the cut paper to the right hand, we move 
the lower part towards the left, about the same distance that 
it was previously slid to the right, we obtain considerable 
variation in the cavities so produced, two long irregular open 
spaces,/,/, Fig. 635, being then formed. This will serve to 
show to what slight circumstances considerable variations in 
the character of the openings between unevenly fractured 
surfaces may be due, such surfaces being moved upon each 
other, so as to have numerous points of contact. 
Most lodes are perpendicular to the horizon, or nearly so; 
but some of them have a considerable inclination or hade,” 
as it is termed, the angles of dip being very va¬ 
rious. The course of a vein is frequently very 
straight; but if tortuous, it is found to be choked 
up with clay, stones, and pebbles, at points where 
it departs most widely from verticality. Hence 
at places, such as a. Fig. 636, the miner com¬ 
plains that the ores arC “ nipped,” or greatly re¬ 
duced in quantity, the space for their free depo¬ 
sition having been interfered with in conse¬ 
quence of the pre-occupancy of the lode by 
earthy materials. When lodes are many fath¬ 
oms wide, they are usually filled for the most 
part with earthy matter, and fragments of rock, through 
which the ores are disseminated. The metallic substances 
frequently coat or encircle detached pieces of rock, which 
our miners call ‘^horses” or “riders.” That we should find 
some mineral veins which split into branches is also natural, 
for we observe the same in regard to open fissures. 
Chemical Deposits in Veins. —If we now turn from the 
mechanical to the chemical agencies which have been instru¬ 
mental in the production of mineral veins, it may be re¬ 
marked that those parts of fissures which were choked up 
Fig. 636. 
