72 The Naturalist in Nicaragua 
their upper portions than below, but to be the effect of the 
decomposition and wearing down of the higher parts, and the 
concentration of the gold they contained in the lode below 
that worn away. We have seen that in the decomposed parts 
of the lode the gold exists in loose fine grains. During the 
wet season water percolates freely from the surface down 
through the lodes, and the gold set free by the decomposi- 
tion of the ore at the surface must be carried down into it, 
so that in the course of ages, during the gradual degradation 
and wearing away of the surface, there has, I believe, been an 
accumulation of the loose gold in the upper parts of the lodes 
from parts that originally stood much higher, and have now 
been worn away by the action of the elements. 
This accumulation of loose gold near the surface of 
auriferous veins, set at liberty from its matrix by the decom- 
position of the ore, and concentrated by degradation, is 
probably the reason of the great richness of many of what 
are called the caps of quartz veins; that is, the parts next 
the existing surface, and has also, perhaps, originated the 
belief that auriferous lodes deteriorate in value in depth. I 
at one time, after having studied the auriferous quartz veins 
of Australia, advocated this theory, which was first insisted 
upon by Sir R. I. Murchison, but further experience in North 
Wales, Nova Scotia, Brazil, and Central America has led me 
to doubt its correctness, excepting in cases such as we have 
been considering, where there has been an accumulation of 
gold in the superficial portions of lodes since their original 
formation. Gold is distributed in quartz veins in bands, 
and in patches of richer stone of more or less extent. These 
richer portions of the lodes, if sunk upon perpendicularly, 
will be passed through, but so also they would be if followed 
horizontally, their extent in one direction being as great as 
it is in the other. The chances of meeting with further 
patches of rich ore in depth, after one has been passed through, 
are about the same as they are in driving horizontally, and 
the frequency therefore with which the auriferous ores are 
met with along the surface will, as a rule, be an index of their 
occurrence in depth, if we be careful in distinguishing deposits 
belonging to the original condition of the lodes, and those 
due to subsequent concentration. To do this we must get 
below the immediate surface, and take as our guide the gold 
