D. Jones — Denudation of Coalhrook-clale. 203 



The same author was astonished to find that a Limestone (Spirorhis 

 Limestone) was in the southern portion of the Coalfield only 170 feet 

 above the base of the Coal-measures, and suggests as an explanation 

 that about Broseley the formation was apparently littoral, and says, 

 " the connexion of the strata between this locality and those where 

 marine remains^ occur is not clearly ascertained," for he had not 

 been able distinctly to detect the band of limestone on the north side 

 of the Severn. He further says, " Nevertheless, by tracing the pro- 

 longation of the bed by means of a few of the associated strata, its 

 equivalents in other parts of the Coal-field may be approximated to. 

 Accordingly, at New Hadley and Wombridge, the place which the 

 freshwater stratum would hold, may be somewhere about that 

 occupied by the marine deposit of Chance Pennystone." Now, con- 

 necting this with the observation about littoral deposits, I suppose 

 he meant that a change of character, from freshwater to strictly 

 marine, took place in the stratum as it passed from the shore, where 

 rivers may have flowed in, to the deep sea, where only marine 

 animals could exist. The Spirorbis Limestone is now known to be 

 of marine origin ; and, again, its geological position would be many 

 yards above the Chance Pennystone. At Hemans Pit this Limestone 

 is 105 feet above the Pennystone, whereas at Lodgewood we have 

 Chance Pennystone 283 feet above the Main Pennystone, the Spirorbis 

 Limestone holding a still higher position than the Chance Penny- 

 stone. If Mr. Prestwich could rewrite his most valuable paper — the 

 text-book of all students of the geology of that district — with such 

 corrections and additions as the evidence gleaned since he wrote 

 would make desirable, it would confer a great benefit upon those 

 who take his paper of 1836 as their guide. Indeed, it is the standard 

 work on the subject, and should be corrected and brought down to 

 the present time. 



At page 435 a table is given of the thickness of Coal contained 

 in the ground, and showing the number of beds into which it is 

 divided, with this remark — " In these localities the productive Coal- 

 measures are fully developed, and consequently the difference of 

 total thickness does not arise from the cropping out at one place of 

 beds which exist at another." Now it is this view which I hope in 

 this paper to controvert, for I maintain that the upper strata have 

 been entirely denuded from the southern portion of the Coal-field by 

 the same denuding force as produced the Symon fault described by Mr. 

 Marcus Scott (Journal of the Geological Society, 1861, vol. xvii., p. 

 457). Mr. Prestwich remarks, "The Ironstones thin out in their range 

 southward in descending order ; thus the Chance Pennystone first 

 disappears, then the Blackstone, and others after ; so that at Broseley 

 we find only the Pennystone and the Crawstone, and to the south of 

 Broseley the Crawstone by itself." The same remark holds good 

 with the coals, and the reason why they are not observed to crop 

 out is, that over the denuded older strata newer strata were laid, and 

 covered up the denuded edges of the coal. 



In the Silurian System of Sir K. Murchison we find the Hills-lane 

 ^ The limestone was at that time supposed to be of freshwater origin. 



