Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/372

 A slight 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

Fig. 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. Fur 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 High 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