On the Paragenetic Relations of Minerals. 63 
rocks containing useful minerals disseminated ought to be 
closely examined for lodes, and there is every possibility that 
when found they may contain the minerals in a more con- 
centrated form than the rock. Granite containing dissemi- 
ated tin ore has, when lodes have been found, been advanta- 
geously worked for tin. It is probable that, at some future 
time, an available copper lode may be discovered in the red 
amygdaloid of Zwickau, which contains plates of metallic 
copper of considerable extent, though not abundant enough 
for working. It is probable that a discharge of cupreous 
liquid from lodes into the partly eruptive amygdaloid, as at a 
later period such a discharge must have flowed into the sea, 
from which the rock of the Zechstein formation originated. In 
North Carolina lodes bearing’ gold have been discovered and 
worked, besides the gold in alluvial deposits, and partly 
imbedded in water-worn fragments of rock. 
Even in the chemical composition of minerals there is a 
remarkable association. Almost all minerals containing 
lithia have an admixture of soda and potash; minerals are 
seldom free from soda. Most galenas contain at least traces 
of silver. But in the association of minerals having no che- 
mical relation, resemblance is still more frequent. There 
is no titanite which is not accompanied by an amphibole, 
scarce any epidote without amphibole and quartz. Rutile 
is never without quartz, while it is never associated with 
titanite. From such facts it is possible to decide with 
certainty whether a rock is diorite or syenite, or diabase 
or dolerite, for neither of the latter would contain tita- 
nites or epidotes. Still more striking are the associations 
in lodes in regard either to the chemical elements, or to 
the lode minerals, irrespective of their chemical resemblance. 
Thus, for instance, the association of cobalt, nickel, arsenic, 
and bismuth—of zinc, lead, and silver—of antimony, scheel, 
and even molybdenum—of antimony and gold. 
The association in some instances of large masses of bary- 
tite and fluorite is not only remarkable in itself, but because it 
contains several of the above mentioned groups of minerals, 
in which the metals are in analogous chemical combinations, 
carbonates being abundant. The varieties of pyrites, glance, 
