572 
ELEMENTS OF GEOLOGY. 
stone is changed into granular marble, with a band of ser¬ 
pentine at the junction.^ 
Plutonic Eocks of Carboniferous Period. —The granite of 
Dartmoor, in Devonshire, was formerly supposed to be one 
of the most ancient of the plutonic rocks, but is now ascer¬ 
tained to be posterior in date to the culm-'measures of that 
county, which from their position, and, as containing true 
coal-plants, are now known to be members of the true Car¬ 
bon iterous series. This granite, like the syenitic granite of 
Christiania, has broken through the stratified formations, on 
the north-west side of Dartmoor, the successive members of 
the culm-measures abutting against the granite, and becom¬ 
ing metamorphic as they approach. These strata are also 
penetrated by granite veins, and plutonic dikes, called “el- 
vans.”f The granite of Cornwall is probably of the same 
date, and, therefore, as modern as the Carboniferous strata, 
if not newer. 
Plutonic Rocks of Silurian Period.^ —It has long been known 
that a very ancient granite near Christiania, in Norway, is 
posterior in date to the Lower Silurian strata of that region, 
although its exact position in the Palaeozoic series can not 
be defined. Von Buch first announced, in 1813, that it was 
of newer origin than certain limestones containing orthocerata 
and trilobites. The proofs consist in the penetration of gran¬ 
ite veins into the shale and limestone, and the alteration of 
the strata, for a considerable distance from the point of con¬ 
tact, both of these veins and the central mass from which 
they emanate. (See p. 562.) Von Buch supposed that the 
plutonic rock alternated with the fossiliferous strata, and 
that large masses of granite were sometimes incumbent 
upon the strata; but this idea was erroneous,and arose from 
the fact that the beds of shale and limestone often dip to¬ 
wards the granite up to the point of contact, appearing as if 
they would pass under it in mass, as at a. Fig. 620, and then 
Fig. 620. 
again on the opposite side of the same mountain, as at 5, dip 
away from the same granite. When the junctions, however, 
are carefully examined, it is found that the plutonic rock in- 
* Von Buch, Annales de Chimie, etc. 
t Proceed. Geol. Soc., vol. ii., p. 562 ; and Trans., 2d ser., vol. v., p. 686. 
