EXCURSION II. 73 



exposed iu 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 irregular, and in two 

 or three places thin bands of conglomerate are interposed be- 

 tween the trap and the claystone. The lower portions of the 

 claystone, next the trap, are harder, or converted into horn- 

 stone ; 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 de- 

 scribed 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 

 claystone vein and the great boulder, some running nearly north 

 and south, and others neai-ly east and west. 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 the claystone : it 

 may be connected with the undei-lying trap vein. Another, 

 close to the boulder, six feet and a-half broad, consists in the 

 centre of blue-coloured, rapidly decaying greenstone, and at 

 the sides of a hard crystalline variety of the same rock, stand- 

 ing above the level of the central parts and of the adjoining 

 sandstone. 



37. The celebrated Corriegills boulder (fig. 16), under whose 

 shadow we shall now rest, is of imposing dimensions, and a con- 

 spicuous object from all parts of this coast. A few on the 

 Corrie shore exceed it in size ; but they are close on the edge of 

 the granite nucleus, and we may suppose it quite possible that if 

 Goatfell "shook his giant sides" under some earthquake throe, 



