180 
AMERICAN GEOLOGY. 
twelve inches thick. The enlargement of fissures subsequent 
to the beginning of the metallic accumulation has been men¬ 
tioned already, but the peculiarity in the cases referred to, is no 
doubt due to the nature and composition of the rock. 
The direction of the lead veins is east and west, or rather 
south of east. When north and south they are less productive, 
though exceptions to this statement do occur. The peculiar 
fissured condition of the limestone has produced a great irregu¬ 
larity in the dip of the veins. Instead of dipping regularly, 
and at a constant angle, the dip takes the form of several suc¬ 
cessive offsets. Thus, for a given stratum, the angle of dip 
may be 45°, but in passing to the south it may be more oblique 
or become horizontal, by following the bedding plane between 
two strata, pursuing a route where the difficulties and distrac¬ 
tions are readily overcome. When, however, it has taken a 
horizontal direction, it may pass to the vertical. There is there¬ 
fore great irregularity in the dip or lead of the vein. The fis¬ 
sures of the Cliff limestone usually stop short of the superin¬ 
cumbent limestone, and hence are capped over by the upper 
mass. 
POSITION OF THE ORE, AND THE LEAST THICKNESS OF 
VEIN WHICH CAN BE WORKED WITH PROFIT. 
§ 108. The broken down veins are concealed in reddish clay, 
ferruginous sand, masses of rock, etc. The lead is then obtained 
from these deposits by digging. 
The position of the ore in the vein is often changed, and it 
has been in process of time detached from its walls, and is ob¬ 
tained in pieces varying in size from a pea to those of a thou¬ 
sand pounds weight. 
The width of vein required for working may be profitable 
if it does not exceed half an inch, provided the ground is not 
very hard. It is evident the profits of working a vein depend 
on the character of the walls, gangue, etc* 
