SOME SCOTCH SERPENTINES. 389 



and diallage rock. It is said to be most frequent among the upper 

 beds of chlorite slate, though occurrences of serpentine in small quan- 

 tities accompany the limestones of lona, Glen Tilt, Harris, and 

 Tiree. On the south side of the Grampians it occurs at Cortachie, 

 on the North Esk, but through the North of Scotland its localities are 

 more scattered. (Near Drimnadrochit, near Inverness.) The beautiful 

 serpentine of Portsoy, said to be employed in some of the apartments 

 at Versailles, forms "three vertical bands," one of them enclosed 

 between hornblende rocks, another between hornblende rocks and 

 crystalline limestone, and the third between quartzose talc slate and 

 mica slate, which is covered by beds of limestone, hornblende slate, 

 and talc slate, and the junction of all these rocks is softened by a 

 mutual exchange of ingredients. In Scalpa, an irregular, highly- 

 inclined bed of serpentine, one hundred yards thick, traverses the 

 gneiss promontory of the lighthouse, and exhibits at its boundaries 

 against the gneiss abundance of hornblende crystals, layers of talc 

 slate, and a sublaminated structure. It contains steatite, asbestos, 

 &c. The granite veins here observed traverse both, the gneiss and 

 its included serpentine, and in the latter rock chlorite is added to the 

 ingredients of the vein. 



Serpentine exists in Lewis, and occurs in Shetland in considerable 

 abundance and beauty, both in the Mainland, in Fetlar, and at Brassa 

 Sound in Unst, where it contains chromate of iron in sufficient abun- 

 dance to be of considerable value in commerce. 



Potstone is found in Glenelg, opposite to Skye, and in the ser- 

 pentine of Scalpa. But the most remarkable rock of this kind is 

 found at St. Catherine's, near Inveraray, on the opposite side of Loch 

 Fyne. It is imperfectly slaty, and has been employed in the erection 

 of the Duke of Argyle's mansion ; other localities are the districts of 

 Strathearn and Breadalbane. 



Crystalline Limestone in Scotland. The white crystalline 

 marbles of lona are found in rocks sometimes referred to mica slate, 

 but considered by MacCulloch to be gneiss. The variously coloured 

 marble of Tiree, with its embedded augite and hornblende, lies in 

 alternating gneiss and mica slate. That of Glen Tilt, characterised 

 by accompanying tremolite, lies in a quartzose mica slate associated 

 with hornblende slate. 



Boue, following up the notices of MacCulloch, traces the line of 

 the Glen Tilt limestones to the east and to the west. In the western 

 direction they proceed from Gow's Bridge, crossing the hills at Lude, 

 and tending toward the south, pass through the Glen of Fincastle and 

 across the valley of the Tummel. It is conjectured that limestone 

 of the same range continues by Mount Alexander and the base of 

 Schehallion, from whence it proceeds through Glen Lyon to the side 

 of Loch Tay at the foot of Ben Lawers, reappears in Crien Larich, 

 at the entry of Strathfillaii to the west of East Tarbet, in Knapdale, 

 and the head of the valley of Croe. 



Eastward from Glen Tilt this limestone is traced in the course of 

 the North Esk, and in the valley of the Dee, near Braemar, &c. 



