474 J. Prestwich, Esq., on the 



hill and dale must be ascribed, as before stated, to the disturbances which have 

 traversed every part of the district. 



Whether the change of relative level and the subsequent denudation were 

 effected slowly or violently, are questions too complex for me to investigate 

 in this paper ; but I am tempted to infer, from the superficial obliteration of 

 the faults, that the change in the levels took place under water, and that the 

 surface was long exposed to its action. I would also infer, from the debris of 

 Silurian rocks distributed through the drift, that during its accumulation, cur- 

 rents flowed over the coal-field from the west and north-west. 



Although the remains of Testacea in the gravel are scarce and much 

 broken, still they suffice to prove the identity of the shells with those of exist- 

 ing species, and therefore to establish the recent withdrawal of the waters. 



