148 

 EXCURSION X. 



TO HOLY ISLE. 



69. MAKE choice of a bright and quiet day, and leave 

 Invercloy for Laralash by the mail steamer from Ardrossan. 

 On reaching Lamlash, a boat must be hired to carry you to 

 Holy Isle. The pier having fallen to pieces, the steamer 

 does not stop, and there is no one permanently resident who 

 could be signalled to come off. A few hours will suffice to 

 examine the island, and the charge for a boat is moderate 

 from 6d. to Is. per hour. The basis of the isle all round 

 is sandstone, which rises to the height of 100 to 150 feet; 

 the rest of the mountain, to the height of 1030 feet, is 

 composed of claystone, so that this rock has the thickness of 

 about 850 or 900 feet. On part of the east side, however, it 

 is much less than this, as the sandstone rises there much 

 above its usual height. The rock is of igneous origin, a 

 member of the trap family, and varies in structure from a 

 soft claystone to a compact felspar; the harder varieties are 

 called clinkstone. As in most traps, the prevailing form is 

 prismatic; and on the east and south-east sides of the island 

 columns of great length appear in the high precipices. But 

 the schistose structure is also common; and, as in cases 

 already mentioned at Corriegills, both structures occur in the 

 same mass, the slaty fracture being at right angles to the 

 axis of the prisms; the ends of the prisms first divide into 

 laminae, and the mass gradually assumes the slaty structure. 

 The weathering of the rock is remarkable, and extends to a 

 considerable depth, presenting successive concentric zones of 

 different colours, which have a very pretty appearance in many 

 specimens. The slaty structure itself, in the case of this 

 rock, seems to be but a step in the process of decomposition. 



Various masses of greenstone occur, both as dikes and 



