PHYSICAL PHENOMENA. 
2tj:t 
seats. When we have step by step pursued a long series of 
observations modified by the localities of a place, we love to 
stop and raise our views to general considerations. Do the 
great cavities, which are exclusively called caverns, owe their 
origin to the same causes as those which have produced the 
lodes o: veins and of metalliferous strata, or the extraor- 
dinary phenomenon of the porosity of rocks ? Do grottoes 
belong to every formation, or to that period only when 
organized beings began to people the surface of the globe F 
These geological questions can he solved only so far as thev 
are directed by the actual state of things, that is, of facts 
susceptible of being verified by observation. 
Considering rocks according to tlie succession of eras, 
we find that primitive formations exhibit very few caverns! 
The great cavities which are observed in the oldest granite, 
and which are called fours (ovens) in Switzerland and in’ 
the south of France, when they are lined with rock crystals, 
arise most frequently from the union ot several contempo- 
raneous vsins of quartz,* of feldspar, or of fine-grained 
granite. The gneiss nreseuts, though more seldom, the 
same phenomenon; and near Wimsiedel.t at the Fichtelgc- 
birge, i had an opportunity of examining crystal fours ot 
two or three feet diameter, in a part of the rock not 
traversed by veins. We are ignorant of the extent of 
the cavities which subterranean fires and volcanic agita- 
tions may have produced iu the bowels of the earth in 
those primitive rocks, which, containing considerable quan- 
tities of amphibole, mica, garnet, magnetic iron-stone, and 
red schorl (titanite), appear to be anterior to granite. We 
find some fragments of these rocks among the matters 
ejected by volcanoes. The cavities can be considered only as 
partial and local phenomena; and their existence is scarcely 
any contradiction to the notions we have acquired from the 
experiments of Maskelyne and Cavendish on the mean 
density of the earth. 
Gleichzeitige Triimmer. To these stone veins which appear to be 
of the same age as the rock, belong the veins of talc and asbestos 
in serpentine, and those of quartz traversing schist (Tkonsckiefer). 
Jameson on Contemporaneous Veins, in the Mem. of the Wernerian Soc. 
t In Franconia, south-east of Luchsburg. 
