154 
MODE OF INCREASE. 
which have been so triumphantly deduced 
from the gayer displays of existing life. 
The law of increase by which the animal 
kingdom is maintained in numbers, has no 
counterpart in the mineral kingdom, but 
the mode in which metals are placed in the 
earth has much of the effect which would 
be produced by their actual growth. A 
progressive developement of their substance 
takes place not by reproduction, but by 
successive discovery. 
Minerals yield their riches to each gene¬ 
ration of mankind by the • application of 
patient toil, the supply growls not by accre¬ 
tion of substance but under the hand of 
labour: whilst the quantity is really inex¬ 
haustible by man, it is practically limited 
by the measure of his power at any one 
time. 
The effect of their actual arrangement is 
to call forth the mental and physical ener¬ 
gies of mankind, to require him to visit 
various regions of the earth, to create the 
necessity and supply the medium of com¬ 
merce ; objects which no other disposition 
of these substances could have secured. 
