Natural History of Volcanos and Earthquakes. 265 
also found in positions which shew that they must have risen 
from the interior of the earth, after the formation of the stratified 
tocks, and found their way into fissures, which in many cases do 
hot reach the surface. ‘Thus, granite, syenite, trachyte, the por- 
phyries, the greenstone, and so on, up to the basalts, form dykes 
in the stratified rocks as well as in one another. They also not 
unfrequently appear in beds between the strata of the Neptunian 
tocks. Granites have been forced up to the surface at the most 
widely different periods ; we find them most commonly in clay- 
te, and in the greywacke formation, in gneiss and in mica- 
slate, and they are sometimes connected with other more consid- 
erable masses of granite. Even after the formation of the oolitie 
and chalk groups, they have been ejected; but there are no 
stanitic dykes described as intersecting these rocks. The stra- 
rocks are usually altered in the immediate vicinity of masses 
or dykes of granite; and their stratification becomes indistinct 
and confused. 'The porphyries, like the granites, exist as inde- 
Pendent formations; but these are not so frequent or so exten- 
sive, and are more frequently in contact with more recent stra- 
tified formations than the granites. ‘The trap rocks traverse all 
the stratified rocks from the gneiss and greywacke group, at least 
‘0 the oolites inclusively. ‘The basalts are found in all forma- 
tions, from the transition and secondary rocks to the lignite inclu- 
‘ively, nay, in the newest formations.* 
In general, some alteration in the adjacent rock and some new 
Mineral productions,t are found where such masses have been 
forced up, and large and small fragments of the rock are not un- 
‘ommonly found firmly imbedded in the latter. We may here, 
-Y Way of example, mention the conversion of compact limestones 
Mto marble, exactly as Hall changed limestones by heating them 
n close vessels or under pressure ; and again, the disappearance 
* the black color and the bitumen in the coal sandstone.t 
—, er ee 
Would probably also thks up substances from the melting mass (alkalies) which 
Would serve as a flux. 
: * The combustion of beds of brown coal seems also to have been effected by 
'gNeous fluid masses which had risen from the interior. Thus the remains of such 
“ombustions always oceur in Bohemia, according to Dr. Reuss, (Néggerath Ausflug 
Vol. *xxvi, No, 1.—April-July, 1839. 
