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vein rather than a bed, as it is placed at an angle of about 15 with 

 the sandstone strata. The sandstone dips 12 E. of S. at about 15, 

 while the claystone vein is inclined in the same direction at an angle 

 of about 30. The rock is divided irregularly into prisms by joints 

 perpendicular to the lower surface of the vein, so that the prisms 

 lean back towards the south, giving the appearance, when viewed 

 casually, of a bedding directed northwards. The structure at the 

 upper surface is often schistose at right angles to the joints, or in 

 the direction of the vein. The base is of a uniform texture, of felspa- 

 thic substance, with quartz pieces imbedded. The structure varies 

 from a uniform claystone, or clinkstone, to a small-grained por- 

 phyry. The colour is pale yellow, or yellowish-white ; and at the first 

 view the rock might be taken for a sandstone : it has indeed been 

 described, when seen in its continuation in the adjoining cliff, as a 

 white columnar sandstone (Headrick's Arran, p. 66). The rock on 

 which it rests is a conglomerate; that beneath which it plunges 

 southwards is fine-grained sandstone. The upper surface of the vein 

 is very rough and jagged, with no resemblance to the style of decom- 

 position among sandstones. The breadth exposed upon the shore is 

 between thirty and forty yards. Along the level shore, where the 

 vein rises to the north, its lower surface is exposed in a wide fissure 

 hollowed out of the sandstone by the action of the sea. It is here 

 seen to rest upon a vein of trap, three or four feet thick, and having 

 the same inclination as the claystone. The line of contact is irregu- 

 lar, and in two or three places thin bands of conglomerate are inter- 

 posed between the trap and the claystone. The lower portions of 

 the claystone, next the trap, are harder, or converted into hornstone, 

 the conglomerate is much indurated, and assumes the dark colour of 

 the trap ; while the latter becomes a fine basalt, and is intermixed 

 with the sandstone below, or dispersed through it in lumps. The 

 posterior origin of the trap vein is thus clearly indicated. The 

 appearances are correctly described by Dr. MacCulloch (West. Isles, 

 vol. ii., p. 403), and an illustrative drawing given (vol. iii., plate 

 xxiv., fig. 1). The sandstone overlying the claystone along the 

 south side of the vein is very slightly altered. 



Several dikes traverse the sandstone platform between the clay- 

 stone vein and the great boulder, some running nearly N. and S., 

 and others nearly E. and W. The former seem to shift the latter, 

 producing a change in the direction of more than 20. The dip of 

 the sandstone is also affected by these dikes, being thrown round 

 about 25 towards the west. One of the dikes, sunk more than two 

 feet below the sandstone, and eight inches broad, is lost on entering 



