296 On the Culm-bearing Beds of Devon and Cornwall. 



stone grit and Old Red Sandstone of the English coal-field, 

 which would be common coordinates, if the Possidonia lime- 

 stones of Devon be the true representatives of the Mountain 

 limestone, the Coddon Hill grits both underlying and over- 

 lying the Possidonia limestones? What possible mineralogi- 

 cal analogy did he discover between the floriferous sand- 

 stones, and their sometimes vast slaty partings, and the grits 

 and shales of the upper great coal-field ? Those slaty partings 

 (which would be the duns and grays of the Bristol coal-field) 

 contain, near Launceston, not only as good roofing-slates as 

 any in Cornwall, but schistose limestones with organic fossils, 

 such as prevail mainly in the grauwacke rocks, while the 

 sandstones (of incalculable thickness) are certainly anything 

 but the Pennant or millstone grit. 



In confirmation of what I have previously advanced, within 

 these few days I have discovered the subordinate Coddon 

 Hill grit and floriferous beds constituting an anticlinal axis, 

 throwing off the volcanic ash and clay slate beds or killas on 

 either shoulder. The line of fracture extends from Greeston 

 Bridge, S.E. of Launceston, behind Milton Abbots to Heath- 

 field, N. of Tavistock, where its beds blend with the common 

 mass, showing, as I stated at Birmingham, that the clay slates, 

 &c. of Cornwall are a portion of a great mineral horizon 

 which divides the plant and culm series. No. 9, into an upper 

 and a lower, that great intermediate floor, (which is certainly 

 above the Possidonia limestones) containing the red and black 

 slates and limestones of Bampton, Hockworthy, Holcomb 

 Rogus, and Westleigh on the north, and the entire of the coral 

 limestones and volcanic ash and grit beds on the south. Addi- 

 tional evidences are daily offering themselves from all the new 

 country I am traversing, affording such an accumulation of 

 concurrent testimony, radiating from different sources to a 

 common centre, as must satisfy the most cautious and scrupu- 

 lous judgement of the nether position of the plants and culm 

 of Devon and Cornwall as compared to the mountain lime- 

 stone and its coal-field. I say again, emphatically and con- 

 fidently, that either Professor Sedgwick, Mr. Murchison, and 

 Mr. Weaver are in error, when they maintain the contrary, 

 or the evidence derived from superposition and organic fossils 

 is altogether valueless. The question in dispute, however, 

 hardly requires the accumulated testimony that can be ad- 

 duced. The merest tyro in geology might take his stand 

 on the Chudleigh limestones alone ; and pointing to the little 

 horizon of a mile around him and the rocks beneath him, he 

 would defeat the assaults of a thousand adversaries. 

 I am, Gentlemen, yours, &c., 



launceston, Sept. 19, 1839. D. WlLLlAMS. 



