S86 TBANSACTlONS OP SECTION C. 



same is true, but on a larger scale, in the Symon Fault of the Coalbrookdale 

 Coalfield," and is to be explained, if the above reasons are valid, by the rapid 

 variation in thickness of the Middle Measures, due to the irregular floor upon 

 which tTiey rest, to the consequent sagging of the beds, and also to local sub- 

 aqueous erosion. Further, such partial unconformities or non-sequences would 

 generally indicate the proximity of that marginal fringe where the Upper 

 Measures overlap the Middle, and rest on pre-Coal Measure strata. 



The Middle and Upper Coal Measures of the Midlands record general 

 but intermittent subsidence, with a considerable pause at the end of Middle 

 Coal Measure time, followed by a much more general depression, as shown by 

 the extended and overlapping sheet of Upper Coal Measures. But there is no 

 evidence which I regard as convincing that regional elevation or great erogenic 

 movements occurred until after the Upper Coal Measures were laid down. 



The floor upon which the Middle Coal Measures were deposited along the 

 southern fringe of the Midland Coalfields was a sinking and already folded 

 and denuded' floor, and it is to be expected, therefore, that these measures rest 

 in submerged gulfs and estuaries, which would mean that some, at any rate, of 

 the several coal basins were originally isolated wholly or in part, and their separa- 

 tion is not to be interpreted as due to folding and subsequent denudation. 



Dr. Newell Arber has argued that the Middle Coal Measures of Coalbrook- 

 dale, the Forest of Wyre, and the Clee Hills were deposited in three separate 

 basins, which as regards the Sweet Coal or Productive Measures were never 

 continuous." On the other hand, just as it is certain that the Productive 

 Measures on either side of the South Pennines were originally continuous, so it 

 is probable that as we go northward from this southern fringe the Productive 

 Measures spread out into more extensive sheets. 



Before leaving the subject I should like to make it clear that I do not wish 

 dogmatically to assert that the conditions were exactly as I have just outlined. 

 We want many more careful observations before the case can be proved. But 

 I do submit that the facts so far as known are capable of the interpretation 

 1 have put upon them ; and that such an interpretation is more consonant with 

 the results obtained by workers among the Coal Measures of the Midlands 

 generally than that which has been in vogue since Clarke's paper on the Symon 

 Fault was published. 



The folding and faulting impressed upon the measures after their deposition, 

 as determining the position and structure of exposed and concealed coalfields 

 alike, are obviously of prime importance ; but involved in these movements 

 are those of pre-Coal Measure time. So complex and confused are these com- 

 bined disturbances that our main hope of grasping their salient features and 

 of applying the knowledge to further the development of new mineral ground 

 is to study more closely the tectonics of our already-worked coalfields and their 

 immediate borders. 



As an example of such intensive geological work, I should like to refer to 

 the detailed plotting by Mr. Wickham King of the Thick Coal of South Stafford- 

 shire on the 6-inch maps. For more than twenty years he has been engaged 

 in collecting and tabulating an immense number of levels and other data from 

 colliery officials, and from old and sometimes half -forgotten borings j and he 

 has now produced a contoured map and a model to the same scale, showing in 

 great detail the folds and faults in the Thick Coal. In 1894 Professor Lapworth, 

 to whose initiative this work was due, emphasised the value of such ' plexo- 

 graphic maps ' of coal seams, and predicted that such maps would be drawn in 

 all the coalfields.-" The data obtained in South Staffordshire also enable us to 

 determine, at some places exactly, at others approximately, the shape of the 

 pre-Coal Measure floor and the outcrops of its constituent formations'; and to 

 disentangle, in part, the pre- and post-Coal Measure movements. Thus we get 



" Mr. Wedd has recently described a similar break between the Middle and 

 Upper Coal Measures of the northern part of the Flint Coalfield. (See Summary 

 of Progress of Geol. Surv. for 1912, pp. 14, 15.) 



'' Phil. Trans. Boy. Soc, London, Series B, vol. cciv., pp. 431-437. ' On 

 the Fossil Floras of the Wyre Forest, &c.' 



=» Fed. Inst. Min. Eng., vol. viii., 1894-5, p. 357 



