728 ^GE OF THE GRANITES [Ch. XXXIV. 



south, the four great classes of rocks, the fossiliferous, volcanic, plu- 

 tonic, 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. 754.) 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 pene- 

 trates. 



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

 glomerate and sandstone (No. 3), which are referable to the Old Red 

 formation, 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 (the higher beds of No. 

 4), in which no fossils have been met with. These are perhaps car- 

 boniferous, though it has been conjectured that they may belong to 

 the New Red Sandstone, or at least to some part of the Poikilitic 

 period. All the preceding formations are cut through by the vol- 

 canic rocks (No. 6), which consist of greenstone, basalt, pitchstone, 

 felstone, and other varieties. These appear either in the form of. 

 dikes, or in dense masses from 50 to 700 feet in thickness, overlying 

 the strata (No. 4). In one region, at Ploverfield, in Glen Cloy, a 

 fine-grained granite (5 a) is seen to send veins through the sandstone 

 or the upper strata of No. 4. This interesting discovery of granite 

 in the southern region of Arran, at a point where it is separated from 

 the northern mass of the same rock by a great thickness of secondary 

 strata, was made by M. L. A. Necker of Geneva, during his survey of 

 Arran in 1839. Dr. MacCulloch had long before pointed out that in 

 the granitic nucleus of the north there were two distinct varieties of 

 granite (see diagram, p. 730) occupying separate tracts, both consist- 

 ing of quartz, felspar, and mica, but the crystalline grains in the fine 

 variety being so small as often to impart to it an arenaceous aspect 

 and sandy feel. Prof. Ramsay afterwards traced out the geographi- 

 cal limits of both varieties, and these have since been more precisely 

 defined and laid down on a map by Dr. Bryce, author of a valuable 

 work on the geology of Arran. The last-mentioned observer remarks 

 that the fine-grained kind never reaches so great an elevation above 

 the level of the sea as does the coarse-grained. He also discovered, 

 in 1864, that the fine-grained variety is not entirely isolated, as for- 

 merly supposed, within a boundary of the coarse, but that, on the 

 south side of the nucleus, it comes into contact with the slates, which 

 it penetrates and alters. The same geologist also found that, besides 

 the outlier of fine-grained granite at Ploverfield, there is another 

 smaller outbreak of the same rock to the westward, a quarter of a 

 mile long and from 250 to 300 yards broad. It is called the Craig- 

 Dhu granite, and seems to rise at the junction of the Old Red sand- 

 stone with the Carboniferous strata. 



