Rev. W. D. Conybeare on the South Welsh Coast Basin. Ill 



Letter from the Rev. W. D. Conybeare to Henry Warburton, 

 Esq. respecting the Extent and Quantity of South Welsh Coal. 



My dear Sir, 



I trouble you again with a few lines, Dr. Buckland 

 having written to me, wishing to have my opinion as to the 

 extent and quantity of the South Welsh Coal. As he re- 

 quired a speedy answer, I was obliged to give him a somewhat 

 vague one ; but having reconsidered the subject, I will ex- 

 plain to yourself more in detail my data and my mode of ap- 

 plying them in the calculation. 



1. I consider our coal as conveniently subdivisible into 

 three series : the first, in the shale below the Pennant, being 

 that worked around our iron- works at Merthyr, &c. The 

 coal above this may be divided into the middle series, be- 

 tween the former and the third or the upper series, very well 

 worked in Monmouthshire. Now as to the thickness of these 

 series ; for the lowest, I may mention the following sections : 

 Vale of Gwaundreth, 47 feet ; Aberdare (only the inferior 

 members of this section worked), 25 feet ; Aberpergwm 

 (only part of the series worked), 41 feet; Merthyr, 58 feet; 

 Tredegar (only part of the series), 39 feet ; Pontypool, 44 feet ; 

 Risca (only part), 30 feet ; Garth-hill (only part), 34| feet; 

 Llanharran, 68 feet. From these data, which are from distant 

 points throughout more than two-thirds of its range, I may 

 safely consider the average thickness of this lower series of coal 

 underrated if I take it at 35 feet. For the middle and upper 

 series, I have not such good or numerous data, but 1 am sure 

 they will be underrated if I take the former at 15 feet, the 

 latter at 10 feet, which will be 35+ 15 + 10 = 60 feet in all. 

 Martin makes them amount to considerably more, namely, 

 95 feet, and I hardly think he is in excess, but I am anxious 

 not to overstate the matter. 



Next as to the extent of these beds. — With regard to the 

 structure of the cr)al-basin, 1 have only one very important 

 addition to make to Martin's description ; namely, that an 

 anticlinal line, throwing up the beds, traverses a great part 

 of it longitudinally, ranging almost due east from Aberavon, 

 half a mile north of the mouth of the Avon, by Cefn Eglwy- 

 sillan, two or three miles north of Caerphilly, a little beyond 

 which it expires. This anticlinal line is of mineral importance, 

 because it either throws up, quite to the surface, the lowest 

 shales, which are the princijjal seat of both the coal and iron 

 ore, as is the case at Aberavon and Dyflfiyn Llynfi (where new 

 works have accordingly been lately instituted), or it brings 

 tliose shales throughout its course within attainable depth ; it 



has 



