1815.] Geological Society. 151 



read, describing certain specimens presented by him to the Society. 

 They consist of two series : one exhibiting the junction of sand- 

 stone and of trap at the Kinnoul, near Perth ; the other exhibiting 

 a similar junction occuningin Salisbury Craig, near Edinburgh. 



A paper by J. Macculloch, M.D. V. Pr. G.S. entitled Observa- 

 tions on the Mountain Cruachan, was read. 



Cruachan, the highest of a cluster of mountains resembling each 

 other in external form and geological composition, is situated in the 

 east bank of the river Awe, between Loch Awe and Loch Etive. 

 Instead of the rugged forms and rough faces that characterize the 

 hills of mica-slate, situated to the south of this district, and forming 

 the basins of Loch Lomond, Loch Lang, and Loch Fyne, it pre- 

 sents a more uniform flowing outline, a more complete covering of 

 herbage, and a less serrated summit, which at the same time is 

 strewed with heaps of fragments. On a near approach the rolled 

 stones which abound in the beds of the torrents appear to be almost 

 entirely composed of granite and porphyry ; but the rock which 

 appears in situ forming the lower part of tlie mountain in schist. 

 This schist sometimes assumes the appearance of a compact mica- 

 slate, but generally of clay-slate, the colour of which varies, from 

 dark lead-grey to pale greenish-grey. Innumerable veins of granite 

 and of syenitic granite of various sizes traverse the schist in all 

 directions ; sometimes passing clean through it, sometimes inter- 

 mingled with it, or involving fragments of it. The schist is often 

 excessively curved and contorted ; and at the points of junction 

 with the granite is either indurated and converted into lydian-stone, 

 or appears insensibly melting, as it were, into the granite, and 

 assuming the character of hornblende-slate. 



The schist does not appear to reach above one-third of the entire 

 height of the mountain ; but nearly half of the remaining ascent is 

 thickly strewed with loose rocky masses, and it is not till these have 

 been surmounted that the crags and precipitous faces of granite 

 begin to show themselves. This granite nearly resembles that of 

 Carngorum, being composed of reddish felspar and white quartz in 

 nearly equal proportions, with a small intermixture of mica : that 

 which composes the summit strongly affects the magnetic needle. 



Veins of compact felspar-porphyry make their appearance in great 

 abundance in this granite : this breadth varies from three or four 

 feet up to 40 or 50, or more ; they are nearly vertical, but run 

 horizontally in all directions. They traverse not merely the granite, 

 but the schist likewise, and even the granite veins of the schist, 

 diH'ering remarkably, however, from these last in occasioning no 

 disturbance in the strata through which they pass, nor intermixing 

 in the least degree cither with the granite or with the schist. 



Besides the veins of granite and of porphyry, are veins of a grey 

 trap rock, and others of a perfectly characterized basalt. 



Similar appearances to these now described occur in the adjacent 

 districts of Midloin, of Argyle, and of Olenco. 



