' 



104 Present State of the Devonian Question. [January, 



VI. REMARKS UPON THE PRESENT STATE OF 



THE DEVONIAN QUESTION. 



By Horace B. Woodward, F.G.S., 



Geological Survey of England and Wales. 



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NE of the most interesting questions that has of late 

 years perplexed the minds of geologists, and one 

 which we might almost say has been a vexed point 

 ever since the district was studied, is the age and relations 

 of the slaty rocks and limestones of West Somerset, Devon, 

 and Cornwall. Originally called " Greywacke " and transi- 

 tion slates, the beds below the culm-measures or true coal- 

 measures were subsequently called " Devonian," and re- 

 garded as the marine equivalent of the old red sandstone. 

 Latterly this classification has been called into question, 

 and it has been urged that the greater part of the Devonian 

 rocks are of lower carboniferous age. This last opinion 

 being a matter of great dispute, it may be interesting to 

 review the present state of the question. 



Upon glancing at a geological map of the country, such 

 as Greenough's, we find that part of Devon north of Barn- 

 staple and South Molton, and that part of West Somerset 

 which includes Exmoor Forest, the Brendon and Quantock 

 Hills, to be coloured a uniform tint as Devonian, corres- 

 ponding to that of the old red sandstone of the Mendips, 

 South Wales, and Herefordshire. This area of the Devonian 

 rocks is bounded on the south by the culm-measures or car- 

 bonaceous series, and the boundary line between the two 

 formations is marked on either side by narrow and appa- 

 rently impersistent bands of limestone, which, to judge from 

 the map alone, would appear to bind them together in con- 

 formabihty. 



Until the late Mr. Jukes brought forward his views upon 

 the subject, the age of these formations was generally looked 

 upon in this way — that the Devonian rocks represented in 

 time the old red sandstone, and that the culm-measures 

 were of carboniferous age, newer than the mountain lime- 

 stone. In Greenough's map these latter were coloured as 

 the representation of the millstone grit, and the same is the 

 case in Ramsay's geological map of England and Wales. 



This apparent indecision as to the true age of the culm- 

 measures has necessarily caused much obscurity when the 

 relations of the two series, and their generally acknowledged 

 conformability, have been taken into consideration. 



