340 The Rev. D. Williams on the Killas Group of 



The sections afforded by the Torbay coast on one side,and 

 by the Dart and intermediate country on the other, also clearly 

 show that the Torquay and Yalberton limestone (part of the 

 outer zone of a great curve) are conveyed to Churston Fer- 

 rers and Brixham by flexure and undulation: these limestones 

 become of very attenuated dimensions at Ditsham, Corn- 

 worthy, and Harberton ford west of the Dart, and are re- 

 presented further westward by a broad, calcareous, and often 

 abundantly fossiliferous band of grits and arenaceous schist, 

 apparent at Staddon point, and north of it in Plymouth sound, 

 at Hessenford, at East and West Looe, Fowey, Gorran, Car- 

 hayes, Veryan, and Gerrans bay, and probably at Watergate 

 bay on the north coast. 



This member of the killas group, considerable as it is there, 

 is of insignificant dimensions on the east, compared to its vast 

 development on the west, where it is evidently augmented 

 by the introduction of new terms derived apparently from 

 local volcanic vomitories, the mud, ash, and elvan dykes, 

 whose contents even now, in numerous instances, show striking 

 affinities with the adjacent schists; the relative scarcity of 

 ash, mud, and porphyry dykes on the east, is attended by a 

 corresponding absence of much of the great schistose masses 

 on the west, and by a greater preponderance of red and gray 

 grits; whereas the gradually-increasing frequency westward 

 of the ash, schist and porphyry dykes, such as are seen from 

 Redding point (west of Plymouth sound) to Cawsand, and 

 abundantly elsewhere, is accompanied by augmenting inter- 

 polations of schistose matter (commonly however of an arena- 

 ceous character), and by less frequent beds of sandstone, al- 

 though the red and gray grits of St. Agnes beacon, or the 

 eastward clifi's of the Helford creek under Mawnan, would 

 suffer little in comparison with their cognate and congenerous 

 deposits at Cockington and Windmill hill near Torquay. 

 Nos. 3 and 4 killas, in fact, at either extremity, may be said to 

 be adjusted together like a solid parallelogram cut into two 

 wedges, the thin edge of the one being fitted against the broad 

 head of the other. 



This series to the eastward forms a portion of the outer zone 

 of a great triple series of parallel concentric curves, the inner 

 one of which, composed entirely of the floral or carbonaceous 

 rocks, conforms perfectly to the south-east outline of the 

 granite of Dartmoor, and in consequence (taking about its 

 middle terms) it ranges from Cockington near Torquay, by 

 Cornworthy on the Dart, to Morleigh, Black-Down, the 

 south of Modbury, Holbeton, and Staddon and Redding 

 points on either side of Plymouth sound : west of the latter 



