288 LYELL'S ELEMENTS OF GEOLOGY. 



Granite of Carbonifer ous and Old Red Sandstone Period. 



A considerable mass of syenite, in the Isle of Sky, is de- 

 scribed by Dr. MacCulloch as intersecting limestone and shale, 

 which are of the age of the lias.* The limestone, which, at a 

 greater distance from the granite, contains shells, exhibits no 

 traces of them near its junction, where it has been converted 

 into a pure'crystalline marble.f 



At Predazzo, in the Tyrol, secondary strata, some of which 

 are limestones of the Oolitic period, have been traversed and 

 altered by plutonic rocks, one portion of which is an augitic por- 

 phyry, which passes insensibly into granite.- The limestone is 

 changed into granular marble, with a band of serpentine at the 

 junction.:]: ' 



Carboniferous period. — The granite of Dartmoor, in Devon- 

 shire, 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 county, which, from their position, 

 and as containing true coal-plants, are regarded by Professor 

 Sedgwick and Mr. Murchison as members of the true carbonife-- 

 rous series. This granite, like the syenitic granite of Christi- 

 ania, has broken through the stratified formations without much 

 changing their strike. Hence, on the north-west side of Dart- 

 moor, 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 elvans."§ The granite of Cornwall is probably of the 

 same date, and, therefore, as modern as the Carboniferous strata, 

 if not much newer. 



Old Red sandstone period. — The plutonic rocks of the Mal- 

 vern hills, in Worcestershire, consist of a granitic compound of 

 quartz, felspar, and hornblende, or occasionally of quartz, mica, 

 and felspar, which passes into syenite and greenstone. |j This 

 rock has altered the adjacent Silurian strata into well character- 

 ized metamorphic schists, principally chloritic and micaceous- 

 schist, with some gneiss, and has dislocated and reversed the 

 position of the beds of the Silurian and Old Red sandstone. 

 There are indications, says Mr. Murchison, of several periods 

 of movement, by which the strata were forced up and folded 

 back, but the chief outburst was after the accumulation of the 

 Silurian and part of the Old Red system, and anterior to the for- 

 mation of the coal-beds, which are undisturbed.lT 



* See Murchison, Geol. Trans., 2d series, vol. ii. part ii. pp. 311 — 321. 



t Western Islands, vol. i. p. 330. plate 18. figs. 3, 4. 



X Von Buch, Annales de Chimie, &c. 



$ Proceedings of Geol. Soc, vol. ii. p. 562. 



II Mr. L. Horner, Geol. Trans., 1st ser., vol. i. p. 281. 



^ Silurian System, p 425. 



