. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. XXXIV.] CARBONIFEROUS AND SILURIAN PERIODS. 725 passes insensibly into granite. The limestone is changed into granu- lar marble, with a band of serpentine at the ;* 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 ascertained to be posterior in date to the culm- measures of that country, which from their position, and as containing true coal-plants, ar
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. XXXIV.] CARBONIFEROUS AND SILURIAN PERIODS. 725 passes insensibly into granite. The limestone is changed into granu- lar marble, with a band of serpentine at the ;* 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 ascertained to be posterior in date to the culm- measures of that country, which from their position, and as containing true coal-plants, are regarded by Professor Sedgwick and Sir E. Mar- chison as members of the true carboniferous series. This granite, like the syenitic granite of Christiania, has broken through the strati- fied formations without much chano'ino; their strike. Hence, on the northwest side of Dartmoor, the successive members of the culm- measures abut against the granite, and become metamorphic as they approach. These strata are also penetrated by granite veins, and plutonic dikes, called " ; f The granite of Cornwall is probably of the same date, and, therefore, as modern as the Carboniferous strata, if not newer. Silurian Period.—It has long been known that the granite near Christiania, in Norway, is of newer origin than the Silurian strata of that region. Yon Buch first announced, in 1813, the discovery of its posteriority in date to limestones containing orthocerata and trilobites. The proofs consist in the penetration of granite veins into the shale and limestone, and the alteration of the strata, for a considerable dis- tance from the point of contact both of these veins and the central mass from which they emanate. (See p. 715.) 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 limesto
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