62 On the Paragenetic Relations of Minerals. 
barytite, fluorite, and brownite. With regard to quartz, it is 
very remarkable that it is almost entirely absent in those 
lode formations which cut rocks consisting of silicates with- 
out quartz. The quartzy sandstone fragments inclosed in 
decidedly igneous rocks is fritted (Buchite), but lode quartz 
has never been found in this state ; a fact which leads to the 
opinion that it has been formed in the wet way, and indeed 
that it has frequently been brought from the interior of the 
earth by steam, and derived from the adjoining rocks by ex- 
traction. The not unfrequent disintegration of the adjoining 
rock speaks in favour of the latter view, as does the presence 
of quartz in the small vesicular cavities of the amygdaloid 
rocks. In this respect lodes and vesicular cavities have a 
great resemblance. 
Some minerals which occur in lodes, especially oxides, are 
not unfrequently accessary constituents of crystalline rocks, 
both sedimentary and eruptive, ¢.g., magnetic iron, titanium, 
tin ore, dyschorite, and tantalite. Some other oxidized 
minerals are still more frequently met with only in lodes. 
Manganese, brown iron ore, red iron, specular iron, have 
never been found in any crystalline rock. The first has 
never been found in a vesicular cavity, nor indeed the latter, — 
with the exception of some few rare minerals containing 
repoxide of iron. Manganese, tin ore, wolframite, &., have » 
never been found with a zeolite, and in the study of the para- 
genetic relations of minerals negative facts must be taken 
into account as well as positive ones. It cannot be denied 
that the minerals disseminated in rocks, such as pyrites, 
especially ferruginous pyrites, and perhaps some kinds of 
glance, and even zinc blende, occur principally in the proxi- 
mity of lodes. It has already been shewn that some of 
these phenomena are owing to the presence of lodes, to im- 
pregnation, but it is also probable that such impregnation 
has taken place when we are unable to detect any direct 
evidence of it. For example, the fact that such pyrites have 
never been found in vesicular cavities, appears to support 
this conjecture. It is indeed possible that not only are tin 
ore, dyschorite, ferruginous pyrites, impregnations of this 
kind from lodes, but likewise gold and copper. In any case, 
