636 Professor Sedgwick and R. I. Murchison, Esq., on the 



second, and occupies a great superficial area ; extending in length, from the 

 plains of the new red sandstone, in the drainage of the Ex, to the western 

 cliffs of the county ; and in breadth, from the southern limits of the second 

 region (as above described) to the northern flanks of Dartmoor and the hilly 

 country S.W. of Launceston. The northern limit of this great area is there- 

 fore sufficiently well-defined for our present purpose. Its southern limits are 

 not so easily described ; the strike of the beds having (through a considerable 

 extent) been interrupted and distorted by the protrusion of the Dartmoor gra- 

 nite; we may, however, state in a few words, — that the western extremity of 

 the boundary-line runs into the sea immediately to the south of Boss Castle 

 harbour, in the county of Cornwall, and ranging thence in a direction bearing 

 a little to the south of east, it passes about a mile and a half to the south of 

 Launceston, crosses the Tamer still further to the south, and just skirting 

 the great mining-field north of Tavistock, abuts against the granite of Dart- 

 moor. Prom this junction, the boundary-line is defined by the northern and 

 north-eastern edge of the granite as far as the Bovey basin. The remainder 

 of the line, from the Bovey basin, round the north end of Haldon, to the drain- 

 age of the Ex, is too complicated to admit of a clear description without the 

 help of a good map. But the deposits of the third region are not confined to 

 the limits here indicated, as they form an outlying mass resting on the lime- 

 stone to the south of Newton Bushel*. 



The whole of the great area inclosed between these boundaries is occupied 

 by rocks of one formation, the greatest part of which are thrown into violent 

 undulations, exhibiting an incredible number of anticlinal and synclinal lines, 

 generally running, with thestrikeof the beds, nearly east and west. These con- 

 tortions are not merely seen in the clilfs and quarries, but they have produced 

 an impress on the whole surface of the region ; which, without containing 

 any hills of great elevation, is thrown into an almost continuous succession 

 of undulations, resembling the waves of a tumultuous sea. These characters, 

 however, disappear near the northern and southern boundaries of the region, 

 where the beds generally acquire a more steady dip, and, as we shall hereafter 

 show, form the bottom of a great trough, so as to repose on all the other stra- 



* The whole south boundary of the culm-measures was re-examined, by one of the authors, in 

 1836, after the Bristol meeting above mentioned. To the N.E. of the Newton limestone (and 

 beyond the limits of this outlier) he found the older fossiliferous slates stretching towards Dart- 

 moor. Hence he concluded, that the culm-measures did not extend, on the flanks of the Dartmoor 

 granite, to the south of the Bovey basin. Since that time, however, Mr. Austen has traced, and 

 laid down on a map communicated to the Geological Society, a considerable band of the culm 

 series, skirting the granite from the north-west end of the Bovey basin to_ the hills west of Ash- 

 burton and Buckfastleigh. 



