
252 STRUCTURAL AND FIELD GEOLOGY 
from a lode. On the other hand, the walls have often been 
rendered excessively hard by the infiltration of silica. Many 
lodes as they are followed downwards show only one wall, 
usually the footwall. In place of a definite hanging-wall, we 
may have a considerable breadth of much shattered and 
jumbled rock, the fissures between the separate blocks and 
fragments being sealed-up with veinstone and ore (see Fig, 
88, p. 240). In other cases walls may become obliterated, 
as it were, by the gradual passage outwards of veinstuff and 
ore, which seem to merge insensibly into the country-rock. 
In yet other cases no definite walls can be traced, and a 
central fissure may or may not be seen. This is often the 
case with zmpregnatzons, to which reference will presently be 
made. As arule, when the fissure occupied by a lode is a 
normal fault, one or both walls are well defined. The rocks 
on the downthrow side of such a fault are often highly 
shattered, while those on the upcast side are usually not 
much broken. When such a fault, therefore, is subsequently 
occupied by an ore-formation, it is the hanging-wall rather 
than the footwall that tends to be ill defined. When a lode 
shows no definite walls, the original fissure is more frequently 
a simple rent than a true fault. 
The ores and veinstones of a lode frequently invade the 
country-rock not only as impregnations, but as sheets (/lazs) 
and subordinate veins. These may be looked upon as 
merely extensions of the lode. Sometimes they penetrate 
the country-rock along planes of bedding, of cleavage, or 
foliation ; in other cases, they obviously follow the subordinate 
cracks and rents which so often accompany faults. 
Stockworks.—Now and again a mass of rock which may 
consist of sedimentary, of igneous, or of schistose materials, 
may be very much jumbled or crushed, and traversed by an 
infinity of minute, reticulating joints and fissures. This, as 
already mentioned, is not infrequently the case with the 
country-rock traversed by some lodes. But highly fissured 
rock-masses are not necessarily connected with great lodes, 
Rocks of various kinds tend to be more or less abundantly 
jointed while they are becoming solidified. This is markedly 
the case with plutonic rocks which have consolidated from 
a state of igneous fusion. Fissures of contraction formed in 

