414 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 22, 



Ashton and Dunsford, the direction of the bedding being south-west 

 and north-east. The beds are broken through on the west by the 

 granite of Dartmoor, and on the east by the limestone of Whiteway 

 and IJppercot. Grits and volcanic rocks are abundant, the latter 

 corresponding in general position to the similar rocks in the vicinity 

 of Brent Tor ; and near the granite they become crystalline and 

 more or less altered, and lose all trace of their mixed igneous and 

 mechanical origin. 



It is not the intention in this communication to enter into a de- 

 tailed account of the Carbonaceous rocks generally. For a further 

 description of them, reference must Be made to the original memoir 

 by Sir Eoderick Murchison and Professor Sedgwick, in the 5th vol. 

 of the Transactions of this Society (2nd ser. Part 3, pp. 669 et seq.). 

 It is to these authors that we are indebted for having first pointed 

 out the true position of these rocks in the geological scale, when, by 

 means of the included plant- and other fossil remains, they identi- 

 fied them with the Coal-measures of South Wales. 



III. Devonian Rocks. 



1. Beds below the Plymoiiih and Torhay Limestones. — The lowest 

 rocks in the district to which this communication more parti- 

 cularly refers have been upraised around Kingston Down, and, 

 between the granite of Dartmoor and the Tamer, in the vicinity of 

 Buckland Monachorum, Beer Alston, and Eoborough Down, near 

 Bickleigh. On the confines of the moor, around Harrowbridge, 

 Walkingham, and Meavy, the beds dip away from the granite at 

 low angles ; but to the south of Bickleigh Eailway-tunnel, the gra- 

 nite has broken through the bedding, which ranges up to it, at 

 right angles to its margin, with a southerly dip. These beds con- 

 sist chiefly of pale greenish and grey argillaceous slates, sometimes 

 soft and silvery, and often veined with quartz ; but grit seams are not 

 common. Korth of Harrowbridge and Buckland-Monachorum the 

 prevailing dip is to the south-west ; but the country is much disturbed 

 by faults and metalliferous lodes, and southerly and westerly dips 

 are not wanting. 



At Morwellham Quay, on the Tamer, the beds are greatly contorted ; 

 and contortion is also seen in the valley of the Tavy, near Eomans 

 Lee, and on the east of Lumber Bridge ; but easterly dips occur on 

 Morwell Down and about Gul worthy, and north-easterly dips at Mill 

 Hill quarry, thrown ofi" from the granite of Hingston Down. Prom 

 these twin granitic protrusions the beds dip away in all directions ; 

 those on the north, however, become horizontal at Latchley Eord, 

 and then rise gently to the north, but are disturbed at Horse Bridge 

 and Hartwell by a fault which has brought them against the Culm- 

 measures. On the south of the down the beds range from the Tamer 

 by Tiddeford to the north of Callington, with a southerly dip at an 

 angle of from 25° to 30°, and pass under higher beds south of the town. 

 On the south of Beer Perrers and Bickleigh these green and grey 

 slates pass under higher beds, which between Tamerton Foliot and 

 St. Budeaux are partly blue and purple. 



