574 
ELEMENTS OF GEOLOGY. 
or had not yet assumed its complete metamorphic character 
when invaded by the plutonic rock. From this example we 
may learn how impossible it is to conjecture whether certain 
granites in Scotland, and other countries, which send veins into 
gneiss and other metamorphic rocks, are primary, or whether 
they may not belong to some secondary or tertiary period. 
Oldest Granites. —It is not half a century since the doctrine 
was very general that all granitic rocks primitive^ that 
is to say, that they originated before the deposition of the 
first sedimentary strata, and before the creation of organic 
beings (see above, p. 34). But so greatly are our views now 
changed, that we find it no easy task to point out a single 
mass of granite demonstrably more ancient than known fos- 
siliferous deposits. Could we discover some Laurentian 
strata resting immediately on granite, there being no altera^ 
tions at the point of contact, nor any intersecting granitic 
veins, we might then affirm the plutonic rock to have origi¬ 
nated before the oldest known fossiliferous strata. Still it 
would be presumptuous, as we have already pointed out (p. 
464), to suppose that when a small part only of the globe 
has been investigated, we are acquainted with the oldest fos¬ 
siliferous strata in the crust of our planet. Even when these 
are found, we can not assume that there never were anv an- 
tecedent strata containing organic remains, which may have 
become metamorphic. If we find pebbles of granite in a con¬ 
glomerate of the Lower Laurentian system, we may then feel as¬ 
sured tliat the parent granite was formed before the Laurentian 
formation. But if the incumbent strata be merely Cambrian 
or Silurian, the fundamental granite, although of high antiqui¬ 
ty, may be posterior in date to hnoion fossiliferous formations. 
Protrusion of solid Granite. —In part of Sutherlandshire, 
near Brora, common granite, composed of feldspar, quartz, 
and mica is in immediate contact with Oolitic strata, and 
has clearly been elevated to the surface at a period subse¬ 
quent to the deposition of those strata.* Professor Se’dg- 
wick and Sir R. Murchison conceive that this granite has 
been upheaved in a solid form ; and that in breaking through 
the submarine deposits, with which it was not perhaps orig¬ 
inally in contact, it has fractured them so as to form a breccia 
along the line of junction. This breccia consists of fragments 
of shale, sandstone, and limestone, with fossils of the oolite, 
all united together by a calcareous cement. The secondary 
strata at some distance from the granite are but slightly dis¬ 
turbed, but in proportion to their proximity the amount of 
dislocation becomes greater. 
* Murchison, Geol. Trans., 2d series, vol. ii., p. 307. 
