MINERAL VEINS. 
Chapter XXI. 
Advantageous Effect of Disturbmg Forces in 
giving Origin to Mineral Veins* 
A further result attending the Disturbances of 
the surface of the Earth has been, to produce 
Rents or Fissures in the Rocks v^hich have been 
subjected to these violent movements, and to 
convert them into receptacles of metallic ores, 
accessible by the labours of man. The greater 
part of metalliferous veins originated in enormous 
cracks and crevices, penetrating irregularly and 
obliquely downwards to an unknown depth, and 
resembling the rents and chasms which are pro- 
duced by modern Earthquakes. The general 
disposition of mineral veins within these narrow 
fissures, will be best understood by reference to 
our first Section. (PI. 1 . Figs, k 1.— k 24.) The 
narrow lines which pass obliquely from the lower 
to the upper portion of this Section, represent 
the manner in which Rocks of various ages are 
intersected by fissures, which have become the 
Receptacles of rich Treasures of Metallic Ore. 
These fissures are more or less filled with vari- 
ous forms of metalliferous and earthy minerals, 
* See PI. 1, Figs, k 1.— A 24, and PI. 67. Fig. 3. 
