204 GEOLOGY OF ARRAN. 



joints; but the form most frequent is that of rhombic blocks. 

 The surface decomposes into a dark brown layer, from the 

 atmospheric action on the iron of the base. The hills get 

 their name from this circumstance. The rock is well adapted 

 for ornamental purposes, and could easily be procured in any 

 quantity. The porphyry occupies the shore, cutting off the 

 sandstone, and forms considerable cliffs, which exhibit the 

 usual wearing action of the sea, when at its old level. The 

 caves are a shelter for the sea-spleenwort and other good 

 ferns; and one of the largest is often used as a preaching 

 station in connection with Kilmorie Church. The " grave? 

 sweet melody" of the Scottish psalmody here mingles finely 

 with the mellowed sound of the dashing waves. On the 

 S.E. side, towards Slaodridh Water, north of the road, the 

 porphyry is seen to rest on sandstone, which, rising gradually 

 from below it, begins to occupy the lower grounds seaward, 

 the porphyry retiring inland, and ranging across the moor to 

 the Crook-crever burn, where it is associated with claystones. 

 Farther up the Slaodridh Water, there are again found great 

 beds of a similar porphyry, as already described in Excursion 

 XV. The great development of these felstones is a remark- 

 able feature of the south-western portion of the island. 



Leaving Tormore, or King's Hill, and crossing to the 

 Shiskin road, we are in front of the fine-grained granite tract 

 of Glen lorsa, and accordingly we find that here the great 

 proportion of the boulders are of this variety of granite ; 

 while those on the eastern side, and along the southern 

 plateau, are of the coarse variety. This points to a cause 

 locally acting in the direction of the glens : we never find 

 lorsa granite on the east side of the island, both kinds are 

 mingled on the west side (Art. 22). 



If we return to Invercloy on foot, the walk will be varied 

 by passing up Clachan Glen and down upon Glen Cloy. We 

 strike off the main road about a quarter of a mile north-east 

 of Shedok Inn, at the bridge over the Clachan burn, and first 

 examine the curious old effigy in the centre of the small 



