204 D. Jones — Denudation of Coalbrooh-dale. 



Section given as " an instructive example of the succession in one 

 spot where the strata are pretty fully developed." This is not the 

 case, as there are wanting "The Big Flint," "Yard Coal," "Double 

 Coal," "Three Quarter Coal," "Top Coal," " Gur Coal," "Stone 

 Coal," " Foot Coal," and " Fungous Coal," all of which have been 

 denuded. Most of the other remarks on this question in "The 

 Silurian System" appear to be derived from Mr. Prestwich's paper. 



Now if we examine the various pit sections, commencing in the 

 north and proceeding southwards, we shall find there has been a 

 denudation of the older Coal-measures of precisely the same character 

 as that shown to have taken place along the eastern boundary, and 

 known as the Symon fault. For the purpose of showing my views 

 upon a small map, and to avoid the confusion which would arise 

 from having a vast number of lines drawn over the map, even if it 

 were possible to get the exact data requisite to enable me to plot 

 them, I have grouped the seams as they occur in a vertical position, 

 distinguishing each group by a distinct kind of line, thus — 



1. Chance Pennystone. ) '\ 

 Fungous and Gur Coal. ) i See 



2. Top Coal to Yard Coal. \ Explanation 



3. Big Flint Coal, Pennystone, and Sulphur Coal. I on Plate V. 



4. Best Eandle Clod and Little Flint. / 



At the end a list is given of sections grouped according to the seams 

 which they contain. We may thus draw lines which will approxi- 

 mately show the margin or denuded edge of the vertical groups. 



I have been at some trouble in ascertaining whether the denuda- 

 tion took place before or after the dislocations ; because, if before, 

 then my lines would be a nearer approximation to the condition of 

 things ; but if after, then the denuded edges would be thrown for- 

 ward or recede according to the " down-throws" or " up-throws." 

 Mr. Marcus Scott and Mr. Parton have given me data, from which it 

 appears quite certain that the denudation took place long before the 

 dislocations. The Calaminker (a mottled clay of the upper Coal- 

 measures, lining the valley of denudation, called the " Symon fault") 

 and Upper Strata, which were deposited after the denudation, are in- 

 fluenced by the dislocations, which must have occurred necessarily 

 even still later.i 



I have before said, the highest workable stratum of what are called 

 the lower or productive Coal-measures is the Chance Pennystone. 

 We find it in the Donington Wood Colliery, and as far east as the 

 Granville Pit. It is not found south of a line drawn from Ketley 

 to a little south of Snedshill [vide Plate V.). Between Sneds- 

 hill and Prior's Lee its boundary proceeds northwards, to join the 

 stratum near Granville Pit. The Fungous Coal being about 50 feet 

 below the Chance Pennystone, and consequently a little more pro- 

 tected from denudation, it ranges a little outside of the margin of 



1 In this I find my views at variance with those of Mr. Eandall, expressed in his 13th 

 letter to the Mining Journal^ where he says, " The whole of the Coal-strata found in 

 the Halesfield Pits of the Madeley "Wood Company was saved from denudation by 

 the mere fact of its having been let down by faults below the same strata which 

 sufi'ered.from denudation in the neighbouring field of Stirchley," etc. 



