60 On the Paragenetic Relations of Minerals. 
implanted upon most of the previous groups, except the 
titanium and manganese group, and probably the spathic 
iron, tin, cobalt, and nickel-silver group, and that in zech- 
stein, &c. The formation is most considerable when bedded 
in barytite. The enormous quantity of silver ore yielded in 
1477 by the mine Ritter St George, at Schneeberg, was 
situated at the intersection of several lodes of heavy spar. 
The rich ores of Peru, Chili, and Mexico, were mostly found 
in heavy spar lodes, with and without quartz. 
XVII. Barytic Mercury Formation.—Cinnabar stands in 
the same relation to heavy spar as the cobalt and nickel mine- 
rals. This is also true even of the mercurial fahlerz, it being 
older than the heavy spar. ‘This formation is most charac- 
teristic in the rich auriferous sandstone of Rhenish Bavaria. 
XVIII. Zeolite Formation.—Several zeolites occur in 
todes, even in those bearing metallic ores, and their forma- 
tion has taken place during a period more recent than that 
of the other lode substances. ‘Their appearance here is so 
peculiar as perfectly to justify the assumption of a zeolite 
formation. — 
It is remarkable that they occur not only in the more 
recent eruptive rocks, in whose vesicular cavities they are 
especially at home, but also in much older rocks. But in all 
cases, it is probable they can only be products of extraction 
and lateral secretion. The absence of magnesium and iron 
is characteristic of the zeolites, and neither the vesicular cavi- 
ties nor the lodes in which they occur contain at the utmost 
more than a trace of minerals containing these radicals. 
XIX. Phosphate Formation—The minerals mentioned 
when treating of the descension theory belong to this formation, 
but we cannot assume that they were formed at any particular 
period. There is no doubt that many are formed at the 
present time. (Vivianite, pyreneite, wavellite.) It likewise 
appears fit here to enumerate the several species of phos- 
phates, rather than to seek for other groups, especially as it 
is probable that none of the phosphoric acid is derived from 
the adjoining rock, or from the apatite in other lodes. 
The uranites occur in lodes in granite and such as separate 
granite from schistose rocks. Calcareous uranite is accom- — 
