THE TEAPPEAN ROCKS. 31 



south-west coast; the next in extent is that of Dunfion, over 

 the Corriegills shore. A similar rock occupies a small space 

 on the Windmill Hill, over Glencloy, in close connection with 

 the Ploverfield granite. A different variety forms the bold 

 pi-ecipices of Drumadoon, on the west, and the principal mass 

 of Bennan Head, on the south. The largest body of claystone 

 forms the middle and upper portions of Holy Isle, and has a 

 thickness of nearly 900 feet ; extensive beds and dikes of the 

 same substance are met with in Lamlash river and at Black- 

 water-foot; lesser veins and beds in many other places. All 

 of these cut through or overlie the carboniferous formations of 

 the southern section of the island; the northern section, the 

 i-egion of granite, slate, and old red sandstone, is almost 

 devoid of these felspathic rocks ; a few dikes only are met with ; 

 almost all those in this tract being of hornblendic or augitic 

 rocks. The pitchstones also, exclusive of those in the gi'anite, 

 are almost all met with in the neighbourhood of Brodick, 

 and towards Mauchrie Water on the opposite shore. These 

 various felspathic rocks thus seem to correspond pretty nearly 

 on opposite sides of the island, and to have no relation in 

 their position to the granitic nucleus. Neither does there 

 seem to us any good foundation for a generalization put for- 

 ward by some writers on Arran, that rocks of this type are 

 more abundant on the western than on the eastern side of 

 the island. 



Overlying rocks, hornblendic or augitic, occur chiefly over 

 the central and south-eastern portions of the southern 

 plateau, south of the parallel of Lamlash. North of this line 

 they have little horizontal extension ; they merely cap the 

 sandstone in isolated knolls or narrow bands of inconsiderable 

 thickness. The details regarding these, as well as the fel- 

 spathic rocks, will be seen upon the map, and will be more 

 fully noticed in the several " Excursions " which follow. 

 Under the same head we shall notice the changes made by 

 the dikes on the adjoining rocks. 



In Arran, as elsewhere, almost all the dikes are simple 



