Cornwall and South Devon. 335 



These red sandstones (No. 2) are succeeded in an ascending 

 and critically consecutive order by eight other great series of 

 deposits, which severally vary in their mineral types and organic 

 contents, the last or uppermost of which is the Cornish killas. 

 That this great group overlies the floriferous or plant-bearing 

 series, as I have termed them, or the " carbonaceous rocks," 

 as they have been designated by Sir H. De la Beche and 

 Professor Phillips, is as capable of demonstration as any geo- 

 logical fact of superposition on record. The diagrams which 

 I now exhibit 1 have carefully copied from natural sections 

 (almost as simple as those of tabular superposition), which 

 show the killas to rest, as if tranquilly piled, on the plant or 

 carbonaceous beds at Boscastle, Petherwin, Tavistock, &c.&c, 

 and these are confirmed by the same continuous carbonaceous 

 rocks in their most prominent and characteristic mineral and 

 organic types, closely investing nearly the whole of Dartmoor, 

 and underlying the entire killas country on the east, south, 

 and west of it. 



These facts confirm more strongly, if possible, the opinion 

 I have long since expressed*, and I cannot but think they 

 should either be disproved, or their legitimate consequences 

 admitted. 



The killas group naturally resolves itself into four subdivi- 

 sions, which are severally characterized by appropriate mineral 

 types and varying per-centages of organic genera and species : 

 these different members are inseparably linked together on 

 their confines, by a common alternation of beds, and by in- 

 sensible mineral gradations, and in the great natural scale are 

 arranged in the following descending order: — 



No. 4. The Ichthyphorous, or Fish-bearing killas. 



No. 3. The Metalliferous killas. 



No. 2. The Padstow, or Tamar killas. 



No. 1. The Tintagel, or Clymenien killas. 



There is nothing arbitrary or inconstant in this fourfold 

 division of the killas group, though from the several granitic 

 interferences, and other derangements, they oftentimes de- 

 viate considerably in their strike, and present a greater or less 

 amount of surface according to the angle of inclination which 

 their beds exhibit, or according as they may be repeated or 

 not by flexures, and the varying bulk of matter which enters 

 into their composition at different localities : with these limi- 

 tations, and the circumstance that Nos. 1 and 4 are vast 

 sphenoid masses, the former thinning away to nothing up the 



* See " Plausible reasons and positive proofs, showing that no portion 

 of the Devonian system can be of the age of the old red sandstone." By 

 the Author, London and Edin. Phil. Mag. Feb. 1842. 



