Ch. XXXIV.] AGE OF GRANITES OF ARRAN. 583 



at a period subsequent to the deposition of those strata.* Professor 

 Sedgwick and Sir R. Murchison conceive that this granite has been up- 

 heaved in a solid form ; and that in breaking through the submarine 

 deposits, with which it was not perhaps originally in contact, it has frac- 

 tured 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. 



If we admit that solid hypogene rocks, whether stratified or unstrati- 

 fied, have in such cases been driven upwards so as to pierce through 

 yielding sedimentary deposits, we shall be enabled to account for many 

 geological appearances otherwise inexplicable. Thus, for example, at 

 Weinbohla and Hohnstein, near Meissen, in Saxony, a mass of granite 

 has been observed covering strata of the Cretaceous and Oolitic periods 

 for the space of between 300 and 400 yards square. It appears clearly 

 from a Memoir of Dr. B. Cotta on this subject,f that the granite was 

 thrust into its actual position Vv'hen solid. There are no intersecting veins 

 at the junction — no alteration as if by heat, but evident signs of rubbing, 

 and a breccia in some places, in v/hich pieces of granite are mingled with 

 broken fragments of the secondary rocks. As the granite overhangs both 

 the lias and chalk, so the lias is in some places bent over strata of the 

 cretaceous era. 



Relative age of the granites of Arran. — In this island, the largest in 

 the Firth of Clyde, being twenty miles in length from north to south, 

 the four great classes of rocks, the fossiliferous, volcanic, plutonic, and 

 metamorphic, are all conspicuously displayed within a very small area, 

 and with their peculiar characters strongly contrasted. In the north 

 of the island the granite rises to the height of nearly 3000 feet above 

 the sea, terminating in mountainous peaks. (See section, fig. 702.) 

 On the flanks of the same mountains are chloritic schists, blue roofing- 

 slate, and other rocks of the metamorphic order (No. 1), into which the 

 granite (No. 2) sends veins. This granite, therefore, is newer than the 

 hypogene schists (No. 1), which it penetrates. 



These schists are highly inclined. Upon them rest beds of conglom- 

 erate and sandstone (No. 3), which are referable to the Old Red forma- 

 tion, to which succeed various shales and limestones (No. 4) containing 

 the fossils of the Carboniferous period, upon which are other strata of 

 sandstone and conglomerate (upper part of No. 4), in which no fossils 

 have been met with, which it is conjectured may belong to the New Red 

 sandstone period. All the preceding formations are cut through by the 

 volcanic rocks (No. 5), which consist of greenstone, basalt, pitchstone, 

 claystone-porphyry, and other varieties. These appear either in the 



* Murchison, Geol. Trans., 2d series, vol. ii. p. 307. 

 f Geognostiche Wanderungen, Leipzig, 1838. 



