404 ARRAN. GEOLOGY. OVERLYING ROCKS. 



a prismatic one at the bottom, and a schistose near the 

 upper surface. This latter surface is in contact with fine 

 sandstone, while the lower side rests on conglomerate. 

 If the examination of this vein be continued on the flat 

 shore, it is found closely united to a large trap vein, 

 which at first sight appears to form a part of it ; being 

 parallel, and generally in close contact, and running 

 east and west with a common dip of thirty degrees to 

 the southward. The appearances are so peculiar as to 

 deserve a more particular detail and a diagram.* By 

 a minute examination, it will be found that the conglo- 

 merate is occasionally interposed between the two, al- 

 though often so thin as to be scarcely visible. Thus 

 these veins are proved to be independent, and the con- 

 nexion between them incidental. The fine sandstone 

 lies beneath the trap vein, and is much intermixed with 

 it ; the trap appearing to be dispersed in lumps through- 

 out the bed. Although the red colour of the conglo- 

 merate continues unchanged, the sandstone assumes the 

 dark grey colour of the trap. Where the porphyry is 

 in contact with the trap, it is undulated, and acquires 

 an intense degree of hardness. 



About a quarter of a mile further on towards Lamlash, 

 another vein of this substance, still more remarkable for 

 the peculiarity of its structure, occurs. As far as its 

 general appearance and dimensions are concerned, it is 

 so similar to the former as to require no particular detail : 

 I may only remark that it appears of equal breadth on 

 the shore, but somewhat less in the cliff. The appear- 

 ances for which it is solely remarkable, are to be found 

 at its junction with the sandstone on the shore, and are 

 most conspicuous below high water mark; for which 

 reason it should be examined at low water. 



In some places, the sandstone is found to be much 

 indurated at the junction, while the clay stone or clink- 

 stone is softened, as if in a state of decomposition. It must 



* Plate XXIV. %. 1. 



