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



best for the purpose; and the successors of that gentleman, 

 the Messrs. Hollingsworth, being so obliging as to prepare 

 some paper with a little salt added to the sizing material, it is 

 to be hoped, from its requiring no trouble or preparation in- 

 jurious to its surface, that the demand for it will be such as to 

 induce them in future to manufacture it as an article of com- 

 merce. 



If the chemical agents employed be pure, the operator, who 

 keeps in view the intention of each separate process, and either 

 adopting the manipulation recommended, or improving upon 

 it from his own resources, may rely with confidence upon a 

 satisfactory result. 



London, February 1, 1844. 



XLIX. On the Killas Group of Cornwall and South Devon; 



its relations to the subordinate formations in Central and 



North Devon and West Somerset ; its natural subdivisions ; 



and its true position in the scale of British strata. By the 



Rev. David Williams, Corresponding Member of the Boy al 



Geological Society of Cornwall*. 

 T NOW exhibit to the Society maps, coloured geologically, 

 from Bridgewater in Somersetshire to the Land's- end in 

 Cornwall, with a section, from the Foreland on the Bristol 

 channel to Lantioc bay, east of Fowey on the English chan- 

 nel, to show the superposition of the Cornish killas with re- 

 gard to all the subordinate formations with which it is inse- 

 parably associated, and the four natural subdivisions into 

 which it resolves itself by characteristic mineral and organic 

 types, which are persistent throughout their entire range. 

 This great and important classification has forced itself upon 

 me by the constant repetition of the same successions in every 

 traverse I have made of the killas country from sea to sea. 



The innumerable minute details of strike and dip which 1 

 have registered from north to south and from east to west, 

 fully convince me that the Cornish killas in the ascending 

 order crowns a magnificent consecutive series such as I have 

 illustrated on the map and section, a series however (com- 

 plete and perfect as it is in all its particulars) which manifestly 

 constitutes only a part of some vast system as yet unfolded. 



I formerly subdivided the entire group into ten component 

 members, the nethermost of which was the Cannington Park 

 limestone near Bridgewater ; but many circumstances have 

 since induced me to suspect that, though geographically it 



* From the Annual Report of the Royal Geological Society of Cornwall, 

 1843. Communicated by the Author, and with corrections by him. 



