478 CUMBRAY (GREAT). GEOLOGY. 



This is probably the remains of a more extensive portion 

 which has in the lapse of time disappeared ; a conjecture 

 which is strengthened by the remarks that will imme- 

 diately be made on the obvious waste of the sandstone. 



Trap veins are however very abundant, while they 

 are also highly conspicuous, traversing the sandstone in 

 various places, but appearing to be most numerous in 

 the neighbourhood of the ferry. They cross the island 

 in a somewhat north-easterly course, being at times 

 curved, but generally straight. One instance occurs where 

 the vein is bent at right angles, being at the same time 

 of considerable dimensions ; a circumstance very unusual. 

 These veins are of various breadths, ranging from 'six feet 

 to as many yards. They are commonly erect, and often 

 stand high above the surface like walls ; a phenomenon 

 not very uncommon in many of the Western islands. 

 One of them is particularly remarkable for the length 

 through which its course is visible, as well as for its con- 

 tinuous projection along the whole line. 



I have mentioned some remarkable instances of the 

 same fact in Isla and in Jura, where the remains put 

 on the appearance of castles, standing insulated on the 

 sea shore. One very striking example occurs in the 

 former island ; where a vein of this kind is seen traversing 

 an extensive tract of the high land for many miles ; hold- 

 ing an uninterrupted straight course over hill and valley, 

 and resembling, from its length and regularity, those 

 march-dykes which the new division of farms has recently 

 introduced into many of the pastoral districts of Scotland. 

 In Mull, as it was also remarked, and more particularly 

 on the shores of Loch na keal, they are exceedingly 

 conspicuous, from their great regularity, as well as from 

 the height to which they rise above the surrounding soil ; 

 while the partial concealment afforded by the growth of 

 shrubs and the investing ivy, give them in a still greater 

 degree the appearance of works of art. On the eastern 

 shore of the same island, there is to be seen one of the most 



