600 
ELEMENTS OE GEOLOGY, 
invaded by certain trappean and plutonio rocks, such as dio- 
rite, serpentine, and granite, occurring in the same country. 
It was then observed that, in places where the secondary 
formations are unaltered, the uppermost consist of common 
Apennine limestone with nodules of flint, below which are 
shales, and at the base of all, argillaceous and siliceous sand¬ 
stones. In the limestone fossils are frequent, but very rare 
in the underlying shale and sandstone. Then a gradation 
was traced laterally from these rocks into another and corre¬ 
sponding series, which is completely metamorphic; for at the 
top of this we find a white granular marble, wholly devoid 
of fossils, and almost without stratification, in which there 
are no nodules of flint, but in its place siliceous matter dis¬ 
seminated through the mass in the form of prisms of quartz. 
Below this, and in place of the shales, are talc-schists, jasper, 
and hornstone; and at the bottom, instead of the siliceous 
and argillaceous sandstones, are quartzite and gneiss.^ Had 
these secondary strata of the Apennines undergone univer¬ 
sally as great an amount of transmutation, it would have 
been impossible to form a conjecture respecting their true 
age; and then, according to the method of classification 
adopted by the earlier geologists, they would have ranked as 
primary rocks. In that case the date of their origin would 
have been throwli back to an era antecedent to the deposi¬ 
tion of the Lower Silurian or Cambrian strata, although in 
reality they were formed in the Oolitic period, and altered 
at some subsequent and perhaps much later epoch. 
Metamorphic Strata of older date than the Silurian and Cam¬ 
brian Rocks.—It was remarked. Fig. 617, p. 567, that as the 
hypogene rocks, both stratified and unstratified, crystallize 
originally at a certain depth beneath the surface, they must 
always, before they are upraised and exposed at the surface, 
be of considerable antiquity, relatively to a large portion of 
the fossiliferous and volcanic rocks. They may be forming 
at all periods; but before any of them can become visible, 
they must be raised above the level of the sea, and some of 
the rocks which ]Dreviously concealed them must have been 
removed by denudation. 
In Canada, as we have seen (p. 491), the Lower Laurentian 
gneiss, quartzite, and limestone may be regarded as meta¬ 
morphic, because, among other reasons, organic remains 
(Eozoon Canadense) have been detected in a part of one of 
the calcareous masses. The Upper Laurentian or Labrador 
* See notices of Savi, Hoffmann, and others, referred to by Bone, Bull, de 
la Soc. Geol. de France, tom. v., p. 317, and tom. hi., p. 44 ; also Pilla, cited 
by Murchison, Quart. Geol. Journ., vol. v., p. 266. 
