1869.] ORMEROD DARTMOOR GRANITE. 275 



blocks ; " and the observations of Professor Sedgwick and Mr. Enys 

 are there quoted (page 171) to show that the general direction of 

 the lines of joint in Devon and Cornwall is from N.N.W. to S.S.E., 

 and that on the northern part of Dartmoor the granite is also cleaved 

 in lines at right angles to it, or nearly so. Variations from these 

 directions are often seen, and the E. & W, joints occur along the 

 whole of the eastern escarpment ; but my own observations agree as 

 to the general direction of the lines of joint with those above quoted. 

 The general and most simple appearance of a joint is merely that of 

 a crack passing nearly perpendicularly through a rock which is of 

 similar character on both sides ; but the variations are frequent ; 

 and of these a few instances will be given. The joints vary in 

 width from a line to an opening of several inches, where the decay 

 has been great ; and in mineral veins, if they ought to be regarded 

 as occupying joints, the width wiU often be several feet. The joints 

 vary from the perpendicular ; and the east and west joints incline 

 more than the north and south ; and there is no rule as to the direc- 

 tion of the inclination. Sometimes there is a difference in the 

 character of the granite on the opposite sides of a joint. A vein of 

 decaying granite occasionally occurs between compact masses of 

 granite of similar character ; a vein at Carrion Hill, near Moreton 

 Hampstead, is an example of this ; but veins of decaying granite, 

 with hard rock adjoining, often occur, which are not apparently 

 connected with joints. An example may be seen in the cutting to 

 the south of Lustleigh station. A series of parallel joints may 

 occasionally be noticed with a few inches only of rock between 

 them ; and though these portions of rock are alike in general cha- 

 racter, the felspar crystals in each will be placed in different posi- 

 tions. The connexion of joints with mineral veins will not be 

 entered upon, except to notice that the joint not unfrequently 

 passes nearly along the centre of a vein of felspar, where it is 

 marked by a black line of fine schorl, in which case the felspar is of 

 a pink colour. Several of these variations may be seen in the 

 weathered cutting on Mill HUl, near Chagford. The character of 

 the granite by the side of the joints (as mentioned in Report, page 

 190) occasionally appears to be altered; on the surface it is 

 black, often from schorl, and presents a tessellated appearance, 

 caused by minute cracks, which penetrate about an inch deep into 

 the rock. If this coating is removed, the unaltered granite of the 

 district will be seen below. Examples may be seen near Chagford, 

 at Lower Murchington, Mill Hill, and about a quarter of a mile 

 from the town by the side of the road to Moreton. Minor lines of 

 joint, extending only over small areas, occur occasionally. These 

 cross at rather acute angles ; and when the sides of these minor 

 lines of joint have been altered as above mentioned, the granite 

 presents a basaltiform appearance, which, if not carefully examined, 

 may mislead. A good enample may be seen at the base of the 

 north end of West Hey Tor, where the basaltiform beds form a stratum 

 only a few feet in thickness, but many of the joints extend upwards 

 into the overlying rock. These joints are perpendicular. 



