442 SHI ANT ISLtS. GEOLOGY. 



of this character; whereas it is irregularly distributed, 

 and is indeed perhaps most abundant in those which are 

 at the greatest distance from the trap. 



I have remarked that the siliceous schist which is 

 dispersed among the shale at the western end, becomes 

 more abundant towards the eastern extremity of Gari- 

 veilan. It here forms a series of three beds, which may 

 be estimated in the thickest part at twenty or thirty feet. 

 These are covered at the western side by the columnar 

 trap, and when that disappears, they occupy the surface, 

 being then incumbent on a lower mass of the same rock 

 of an irregular form, namely, the peninsular and perforated 

 rock mentioned at the beginning of this description. They 

 are thus contained between two masses of trap, being 

 slightly incurvated and elevated as if to accommodate 

 themselves to the ppsition of those. The uppermost is of a 

 dove colour, having a tendency to a cubical or rhom- 

 boidal fracture, and separates naturally into masses and 

 fragments of these and similar shapes. But when forcibly 

 broken, its fracture is conchoidal ; while at the same 

 time it flies asunder with a violence resembling that of 

 glass, the fragments being scarcely less sharp, and highly 

 sonorous. The next bed consists of the same substance, 

 but possesses a botryoidal or spherical structure similar 

 to that of the shale before described ; towards which 

 structure a slight tendency may also be observed in the 

 uppermost ; particularly on the exposed surfaces. The 

 third and lowest bed is a compact siliceous schist of a 

 purplish grey hue ; as hard and still more sonorous than 

 that first described, and without any trace of the spherical 

 structure. 



Beds of shale similar to those at the west side of < 

 veilan are found in Eilan Wirrey, but of much greater 

 thickness, attaining apparently the height of 100 feet, and 

 surmounted in the same manner by more or less regularly 

 columnar trap. The black botryoidal beds are here both 

 thicker and more remarkable, and the alternations as 



