200 D. Jones — Denudation of Coalhrook-dale. 



east of the I of ''signal" on the Map), and the bottom of the clifi 

 is in the division No. 5. 



The dip lessens, and soon the beds are flat. There are springs at 

 the foot of the cliff, thrown out by the marly bed in No. 5 ; and 

 No. 4 ends off at the top of the cliff about half a mile southward of 

 Holywell. 



From Holywell there is a slight south-westerly dip, so that the 

 lower beds again rise ; and as the level of the ground falls north- 

 eastward No. 5 ends off about a quarter of a mile before getting to 

 the Martello Tower, and there is then nothing but the Chalk Marl 

 (only 50 or 60 feet thick?) above the Upper Greensand. The 

 former is hard at the bottom, and markedly bedded ; the latter con- 

 sists of green-grey and grey sandstone, coarsely bedded, with brown 

 and green nodules in the top part, and is not very distinctly separated 

 from the former. 



Just beyond the Tower the Gault crops out: it is a light-grey 

 sandy clay, calcareous at top, and drying hard ; but only about six 

 feet of it are shown. 



On comparing this section with that of the Kentish cliffs, so well 

 recorded by Mr. W. Phillips,^ there seems to be a good deal of differ- 

 ence between the two chalk-coasts, as may be seen from the following 

 Table, in which the divisions of the chalk in the two are correlated, 

 as nearly as the evidence allows, though without certainty : — 



Kentish Coast. Sussex Coast. 



Margate chalk, with few flints.^ 



Chalk with ( Chalk, with few organic remains... 1. Chalk, with flints. 

 many flints i C^^^'^' ^'^^ many organic remains ) 2. Chalk, with flints and nodular 



^ ■ ( (rough) \ layers. 



Chalk, with few flints ? Absent. 



I Chalk with many organic remains \ 3. Chalk, without flints, but with 

 (rough) j nodular layers. 



Chalk, with few organic remains ... 4. Massive chalk, without flints. 

 Absent, or included in the next below 6. Bedded chalk, without flints. 

 Grey Chalk (or Chalk Marl) 6. Chalk Marl. 



Possibly the highest division of the Kentish Chalk may be un- 

 represented in the Sussex section, and perhaps also the fifth division 

 of the latter may be the equivalent of the upper part of the " Grey 

 Chalk " of Mr. Phillips, which may include more than the " Chalk 

 Marl." 



in. — Denudation of the Coalbrook-dale Coal-field. 



By Daniel Jones, F.G.S. 



(PLATE V.) 



ALTHOUGH the Coalbrook-dale Coal-field has received a large 

 share of the attention of geologists, the progress of mining 

 operations reveals new facts from time to time, enabling us to explain 

 away some of the difficulties which have beset earlier writers. 



^ Trans. Geol. Soc. ser. i. vol. v. p. 16. 



2 Not noticed by Phillips, as it does not occur on the coast he described. See 

 Quart. Journ. Geol. Soc. vol. xxi. p. 395. 



