iS73«] Present State of the Devonian Question. 109 



The precise age of the culm-measures and their relations 

 to the Devonian rocks are points which at first strike one 

 as of great importance. 



The perfect conformability of the northern boundary of 

 the culm-measures with the Devonian rocks has generally 

 been admitted, by Sedgwick and Murchison, and most other 

 geologists. 



In South Devon, however, an unconformability has been 

 pointed between these formations. This was described by 

 Mr. Godwin-Austen, and latterly by Dr. Holl, who remarks 

 that the base of the lower culm-measures does not every- 

 where rest on the same part of the underlying Devonian 

 rocks. He adds, that " this unconformability on the 

 southern side of the culm-trough is so considerable that it 

 throws doubt upon the reality of the apparent regular suc- 

 cession to the north, and leads to the suspicion that the 

 conformability which is there supposed to exist may be more 

 apparent than real." * 



Mr. Jukes, t however, points out that there is really no 

 proof of this unconformability in South Devon, owing to 

 the difficulty in deciding between stratification and cleavage, 

 and the many disturbances to which the beds have been 

 subjected. 



Mr. T. M. Hall, remarking on the Devonian and culm- 

 measures, says — " The two great systems pass quite insen- 

 sibly one into the other, without any distinct line of separation 

 between them."| And this is evident from the sections 

 exposed in quarries and in the cuttings of the new railway 

 between Barnstaple and Taunton, for one passes from one 

 series to the other before one is aware of it ; there is no 

 sudden break or change. 



The age of the culm-measures is now admitted to be that 

 of our true coal-measures. For in the evidence given 

 before the Royal Coal Commission there was some question 

 as to whether the coal-measures likely to be found to the 

 south of the Mendips might not be of the type of the 

 Devonian culm-measures ; and Mr. Etheridge also said that 

 he was inclined to think that the Devonshire coal-field was 

 part and parcel of the South Wales coal-field, the lowest 

 portion of it, but deposited under very different conditions, — 

 an opinion which was indeed arrived at by Sedgwick and 

 Murchison. He thought that the impure coals of the 



* Quart. Journ. Geol. Soc, vol. xxiv., p. 442. 

 f Notes on Parts of South Devon and Cornwall. 

 \ Geology of Lundy Island. 



