Dr. Mac Culloch on the Gra?iitc Tors of Cornwall. 67 



The Logging rock (PL III.') is situated on a peninsula of granite, 

 in the parish of St. Levin, which stretches out about 200 yards into 

 the sea, its isthmus still exhibiting remains of the ancient fortification 

 of Castle Trereen. The mass of granite which forms this peninsula 

 is split both perpendicularly and horizontally by numerous fissures, 

 and is thus divided into a number of cubical and prismatic masses. 

 A similar disposition in all the rocks of this shore has caused them 

 to assume those singular forms which are SO'^ conspicuous at the 

 Land's End. The appearance of the perpendicular fissures on 

 approaching the Logging rock from the isthmus is so remarkable, 

 that we might for a moment fancy it the effect of stratification, as 

 geologists have in other instances been tempted to suppose. Crys- 

 tals of tourmaline are found in this granite, which has supplied the 

 cabinets of collectors with so many specimens, as to be too well 

 known to need description. 



The general height of the mass of rock on which the logging 

 stone is placed varies from 50 or 80 to 100 feet, and it exhibits 

 almost all round a perpendicular face to the sea. It is divided into 

 four summits, on one of which, near the centre of the promontory, 

 the stone in question lies. If the v/hole peninsula be viewed 

 laterally, the conformity of the rocking stone to the mass on which 

 it stands and to the other small stones which crown the summits, 

 is such that the eye cannot delect it, so perfectly it seems in its 

 place. It is in the front view only that it appears detached, as if 

 occupying an accidental and not its natural and original place. Its 

 general figure is irregularly prismatic, and foursided, having at its 

 lower part that protuberance on which it is poised. So inclined is 

 the plane on which it rests, that it appears at first sight as if a slight 

 alteration of its position would cause it to slide along the plane into 

 the sea, standing as it does within two or three feet of the edge of 



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