274 PKOCEEBINGS OF THE GEOLOGICAL SOCIETY. [May 12, 



is, as a whole, a coarse-grained mixture of quartz, felspar, and mica, 

 the latter sometimes white, at others black, the two micas occasion- 

 ally occurring in the same mass. It is frequently porphyritic, from 

 the presence of large crystals of felspar, and here and there schor- 

 laceous ; but the latter character is chiefly confined to the outskirts, 

 where the Dartmoor granite adjoins the slates." This description 

 is very applicable to the southern part of the district, which will 

 now be noticed, where the granite is said greatly to resemble that 

 of Auvergne ; but to the north of the river Teign the rock is more 

 compact and crystalline. 



The apparent stratiform appearance and rapid changes of cha- 

 racter in the beds of granite are so well known to most geologists, 

 that it is not needful to enter upon that point at length. Mr. D. Mack- 

 intosh, in his paper "On Oblique Lamination in Granite" (Q,. J. Gr. S. 

 vol. xxiv. p. 279), mentions instances of the linear structure of that 

 rock on Dartmoor, and the occurrence of striking variations in its cha- 

 racter in overlying parallel beds. De la Beche's report states that " a 

 very general structure prevails throughout the Cornish granites, and 

 is more particularly observable in the large masses. This structure 

 consists in a division of the granite into portions resembling beds, 

 which form tabular masses when they are extensive, the edges 

 bending beneath the adjoining schistose rocks " (page 163). I have 

 observed that the beds also occasionally bend or dip on Dartmoor. 

 Thus, on the north-east side of the Moor, at Scarrey Tor and Higher 

 Belstone Tor, on Belstone Ridge, the beds of granite dip towards the 

 Carboniferous rocks which closely adjoin them on the north-west. The 

 last-named Tor is cut off abruptly at the south-eastern end, and the 

 side of the hill is for a considerable distance covered with angular 

 fragments. Possibly the granite originally dipped also to the south- 

 east, and the beds broken up by the joints have rolled down to the 

 river Taw. Similar curvature has been noticed in places remote from 

 the schistose rocks ; thus, on Teigncombe Common, near Chagford, 

 more than two miles distant from the carbonaceous rocks, the 

 granite at Kestor dips in a northerly, and at Middleton in a south- 

 erly direction — causing probably the contour of the hill, and the 

 valleys of the north and south Teign. At Blackingstone, near 

 Moreton Hampstead, the beds curve down on the north side, pro- 

 bably causing the valley that lies between that rock and the White 

 Rock, where the beds lie nearly horizontally. At Houndtor (about 

 halfway between Chagford and Ashburton) the beds at the west 

 end are nearly horizontal ; at the east end they curve downwards, 

 and probably cause the valley between that and Leign Tor. These 

 are the most obvious examples of " dip" in the granite that I have 

 noticed in the district to which this paper relates ; in all these cases 

 the dip is very perceptible, and quite distinct from oblique lami- 

 naoion. 



The same Report states (page 165) that " it is the intersection of 

 the more or less perpendicular joints or divisional planes with the 

 stratiform structure in the Cornish and Devon granite which gives 

 it the appearance of being composed of a multitude of rectangular 



