Quartz Lodes 69 
forest regions. It has been ascribed, and probably with 
reason, to the percolation through the rocks of rain-water 
charged with a little acid from the decomposing vegetation. 
If this be so, the great depth to which it has reached tells of 
the immense antiquity of the forests. 
_ Gold-mining at Santo Domingo is confined almost entirely 
to auriferous quartz lodes, no alluvial deposits having been 
found that will pay for working. The lodes run east and 
west, and are nearly perpendicular, sometimes dipping a 
little to the north, sometimes a little to the south, and near 
the surface, generally turning over towards the face of the 
hill through which they cut. The trend of the main ranges, 
also nearly east and west, is probably due to the direction of 
the outcrops of the lodes which have resisted the action of 
the elements better than the soft dolerytes. The quartz 
veins now form the crests of many of the ranges, but are 
everywhere cut through by the lateral valleys. The beds of 
doleryte lie at low angles, through which the quartz veins 
cut nearly vertically. Excepting that they are very irregular 
in thickness, and often branch and send thin offshoots into 
the enclosing rocks, they resemble coal seams that have been 
turned up on edge, so as to be vertical instead of horizontal. 
They run for a great distance. Near Santo Domingo they 
had been traced for two miles in length, and probably they 
extend much further. They are what are called fissure- 
veins, owing their origin to cracks or fractures in the rocks 
that have been filled up with mineral substances through 
chemical, thermal, aqueous, or plutonic agencies. In depth, 
the bottom of fissure-veins has never been reached, and 
taking into consideration the deep-seated forces required to 
produce fissures of such great length and regularity, we may 
safely assume that they run for miles deep into the earth— 
that their extension vertically is as great as it is horizontally. 
The probability that they extend to immense depths is 
increased when we reflect that mineral veins occur in parallel 
groups that run with great regularity for hundreds of miles; 
and further by the fact that, in all the changes of the earth’s 
surface, by which deep-seated rocks have been brought up 
and exposed by denudation, no instance is known of the 
bottom of a fissure-vein having been brought by such move- 
ments within the reach of man. 
