620 BEPOET— 1891. 



The Coal-measures are thus estimated at 7,496 feet, or nearly 1^ mile in 

 thickness, besides the Millstone-grit and the Carboniferous or Mountain Lime- 

 stone occupying a stil] lower position. 



Differences of observation or of opinion from time to time have caused different 

 estimates. In 1855 Professor J. Phillips, who took a very strong interest in the 

 geology of the coal-fields, published the following measurements (in his * Manual 

 of Geology,' 1855, p. 201) as representing only a general view, and he indicated 

 that nearly 12,000 feet thickness may occur near Llanelly : — 



Feet. 

 Llanelly series, with several beds of coal . 1,000 



Penllergare series of shales, sandstones, and 



beds of coal— 110 beds ; 26 beds of coal . 3,000 



Central series (Townhill sandstones of Swansea 

 = Pennant-grit of the Bristol coalfield) — 

 62 beds ; 10 beds of coal .... 3,2i6 



Lower shales, coals, and ironstones (Merthyr) 



—266 beds ; 34 beds of coal ... 812 



Farewell Rock and Gower Shales, above the 

 Carboniferous Limestone. 



8,058 



Professor Hull ' gives about 1,200 to the Coal-measures, with twenty-five seams 

 of coal of two feet thickness and upwards ; making a total of eighty-four feet of 

 workable coal. In 1881 Professor Hidl calculated that there remained about 

 32,166 millions of tons of available coal, which might possibly last for more than 

 1,000 years at the present rate of consumption. 



Mr. E. Rogers, in the ' Memoirs of the Geol. Survey : Iron-ores,' Part III., 

 1861, p. 169, divides the Coal-measures of South Wales into an Upper and a 

 Lower series, with the hard siliceous sandstone (locally a conglomerate), known 

 as ' Cockshute ' and ' White Roclis ' between them. The upper measures, he says, 

 are mostly micaceous sandstones, locally known as ' Pennant Rocks.' The lower 

 series is sometimes termed the ' iron-bearing measures,' as it contains the bulk of 

 the ironstone as well as coal, which is bituminous on the east and gradually less 

 and less bituminous westward, until after passing the great dyke or fault in the 

 Vale of Neath it becomes anthracite. The upper series contains few iron-ores, and 

 the coal is bituminous, even when anthracite exists below it, as in the Swansea 

 district and elsewhere. 



In his communication to the British Association in 1837,- Sir W. E. Logan 

 stated that ' the non-bituminous coal, or stone-coal, is found on the north side and 

 at the west end ; the bituminous coal on the south side and east end ; and that 

 there is an intermediate region occupied by an intermediate quality.' These 

 conditions of the coal-seams indicated to Logan ' the possibility of a rule in the 

 change of quality — namely, that it occurs in parallel planes, cutting the seams of 

 coal without regard to their strike or inclination, and dipping to the soutli or east 

 of south.' 



These coals begin to become anthracitic at Rhymney ; and the change becomes 

 gradually more and more marked as we pas9 by Dowlais, Cyfartha, Hirwain, 

 Onlwyn, and Neath Talley, to the Swansea Valley,^ according to analyses given 

 ty Mr. David Mushet in the Appendix to his ' Papers on Iron and Steel,' 8vo., 

 London, 1840. At page 68 of this book Mr. Mushet notes that ' in South Wales 

 as the coals approach the anthracite district they are found to contain 90 per cent, 

 (of carbon), with no more flame than is necessary to convert the coal into 

 coke.' 



Mr. Etheridge (1885) accepts (p. 238) Professor Phillips's foregoing table ; but 

 he also arranges the coal-bearing portions as divisible into — 1. Upper Pennant 



' The Coalfields, &c., 1881, p. 108. 



* Report, 1838, Trans. Sect., p. 85. 



* Bevan, Geologist, vol. ii., 1859, pp. 78, 79. 



