GENERAL OUTLINE OF THE STRUCTURE. 7 



sedimentary strata. These and the slates are not repeated 

 on the W. side in like positions, the strata being successively 

 older as we advance in that direction. The slates thus 



, Mineral axis of granite; b fej old slates corresponding on opposite 

 sides of the axis; c c and d d newer slates also corresponding. 



pierced are part of a broad zone of slate rock which traverses 

 Scotland diagonally from sea to sea, intersects the line of the 

 Clyde shores, and crosses the islands of Bute and Arran. It is 

 usually divisible into thi'ee distinct bands; a lower micaceous, 

 passing into gneiss; a middle dark-coloured clay slate, and an 

 upper green or chlorite slate, the two latter forming what is 

 called the clay-slate series. The newest of the two upper slates 

 is not found in Arran, and is probably either thrown out west- 

 ward beyond the line of bearing of the second slate, or is so 

 altered by the near proximity of the granite as to be undis- 

 tinguishable from the middle or dark-coloured slate, through 

 which the granite has been protruded. On the east side of 

 the granite nucleus, above Corrie, this slate band is extremely 

 narrow ; on the western side it is much broader ; but the 

 lower micaceous band appears only in patches in the promon- 

 tories west of Catacol ; it is not seen in any great body till 

 we pass into Cantire. 



This singular abnormal position of the Arran granite, 

 first pointed out by Dr. M'Culloch, gives to the island all its 

 peculiarities, both as regards its geographical features and its 

 geological structure. The protrusion of so large a body of 

 igneous rock along the line of junction of the older slates 

 and the secondary formations, and its elevation to a great 

 height in a space so limited, might naturally be expected to 

 produce phenomena of varied interest, such as have been 

 alluded to in the opening paragraph (Art. 1). 



