468 J. Prestwich, Esq., on the 



The ballstone is overlaid by a series of thick beds of sandstone, with subordinate shales, and a 

 few limited seams of coal. The lithological characters mark a period of some duration, disturb- 

 ance, and change, with a few intervals of quiet, as during the deposition of the brick measure 

 and the blackstone. In the latter deposit we again find a few marine and fluviatile Testacea 

 associated with land plants. 



At Donnington, the thin bed of fine bass above the blackstone coal contains numerous well- 

 preserved Lingulae, with other marine testacea and remains of fishes, indicating a nearly complete 

 cessation of that fluviatile action, which in other parts of this series.accumulated such quantities of 

 Unios. 



The strong and intermitting fluviatile action was prolonged upwards to the Chance Penney- 

 stone, where another considerable interval of calm occurred, during which marine Testacea again 

 lived and multiplied, as is proved by the abundance of the Leptcena scahricula, associated with 

 a few other marine Testacea and fishes. 



The characters, above described, of the strata between the top coal and the Chance Penneystone 

 are limited to the north of the coal-field, to which the accompanying coals and ironstones are 

 almost entirely confined. 



Above the Chance Penneystone, — the thick preponderating beds of sandstone, — the change 

 in the mineralogical characters of several beds, — the scarcity of vegetable and animal remains, yet 

 evidently with a continuation of a powerful aqueous action, probably resulted from a considerable 

 mutation in the condition of the adjacent land, to which we shall recur shortly. 



It will be now necessary to point out the principal changes of lithological 

 characters and animal reliquiae of the coal-measures in their horizontal range: 



1st. The lower series of coals, up to the Penneystone, are tolerably persistent throughout, 

 from Donnington to Broseley ; but above that stratum, the coals and ironstones, with their asso- 

 ciated marine reliquiae, have a gradually diminishing horizontal range southward, so that the 

 upper beds are limited to a small district in the north of the coal-field. (See Diagram, Plate 

 XXXVIII.) 



2ndly. The absence of organic remains in the Penneystone at Donnington, and the gradual and 

 rather abundant appearance of marine reliquia2, accompanied by a decreasing thickness of the 

 stratum as it trends southward until it disappears at Broseley, deserve special notice. A narrow 

 band of limestone, apparently of fresh-water origin, makes its appearance in that district higher in 

 the vertical range of the measures, 



3dly. Other changes, claiming particular mention, are the presence of numerous beds of red 

 and variegated clays and marls, and calcareous sandstones, in the south-east of the coal-field, 

 and the expansion of many of the shales and sandstones to the northward, with the abrupt 

 thinning out of all the coals and ironstones above the Penneystone between Donnington and 

 Lilleshall, accompanied by an increased importance in the upper series of soft conglomerates and 

 sandstones. 



4thly. It is necessary to mention the great variations of lithological character, and irregularity 

 of range of almost all the arenaceous strata. 



The conclusion, therefore, which I think may safely be drawn is, that the 

 deposition of the coal-measures commenced immediately subsequent to some 

 great convulsion altering the relative level of land and water; and — judging 



