276 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 12, 



A sKght inspection of a tor will in most cases show that the form 

 in which it now appears is caused by lines of joint. In those where 

 the granite is crystalline and hard, as at Yes Tor, East Mill Tor, 

 Belstone Range, Wattern Tors, and others, this is very apparent ; but 



Eig. 1. — South side of North end of Belstone Tors, showing ends of 

 North and South Joints and Dip of Granite to the West, 



in some cases, as at Kestor, where the granite is not very compact, 

 and is subject to decay, this, though not so obvious, is soon detected. 

 A Dartmoor tor consists sometimes of a solitary rock, though more 

 frequently of distinct but associated masses, rising from the same 

 bed or boss of granite. At the tors composed of associated masses, the 

 form of each division can be generally traced with ease to the influence 

 of the joints, and the line followed from rock to rock. At Hound 

 Tor this is well shown. The tor is divided into three portions by a 

 wide opening which traverses it from west to east, and is crossed 

 at part of the eastern extremity by another opening ranging nearly 

 from north to south. There are low broken cliffs on both sides of the 

 east and west opening ; and on the south side of it the oblique 

 beds mentioned by Mr. Mackintosh (Q. J. G. S. xxiv. p. 279) are well 

 exposed. Great Mistor, on the western edge of the moor, is divided 

 in a similar manner by a wide opening ranging from N. to S., with 

 low cliffs at the side. Pur Tor, near the centre of the moor, is a 

 fine example of an associated tor. Hey Tor is divided into East and 

 West Hey Tor by a wide opening which runs nearly from N. to S. 

 At East Hey Tor the east and west joints are very clearly shown 

 dividing it into distinct blocks. It may here be mentioned that it 

 does not appear that these wide openings were caused by the decay 

 of soft rock. Occasionally, as at Hey Tor, the rock that underlies 

 the opening is exposed ; and when that is the case it is generally 

 found that the beds of which it consists are continuous from the 

 adjoining tors. The solitary tors will in most cases be found to 

 have been once connected with others in the same vicinity, though 

 now so far apart that they are known by separate names. Thus 

 Yes Tor is a solitary tor, bounded on two sides by lines of north and 

 south joint, and with the east and west lines easily traceable. This 

 and Iligh Willhayse, about half a mile to the south, and some other 

 smaller rocks, once doubtless formed part of the same field of 

 granite. Kestor and Middletor, solitary tors distant about half a 



