464 J. Prestwich, Esq., on the 



5. Marine, Terrestrial," 



} 



T'l • 1 ( White flat stone. 



I'luviatile 



Terrestrial To flint coal bas. 



6. Marine'? or Fluviatile. Flint-coal bas. 



Terrestrial Flint-coal and underlying sandstone. 



7. AfarineandFluviatile? Penneystone ironstone. 



Terrestrial and Fluviatile. Strata below the Penneystone to the base of the coal-measures*. 



These alternations necessarily lead to the inquiry — whether they were pro- 

 duced by oscillations of the land, whereby it was at one time submerged and 

 covered with a stratum of silt containing- marine exuviae, and at another raised 

 and converted into a marshy tract, overspread with a thick, luxuriant vege- 

 tation, and harbouring in its shallow waters numerous freshwater shells, to be 

 again submerged and overlaid by another marine deposit, — or whether the 

 phenomena cannot be accounted for by supposing, that the coal-measures were 

 accumulated in an estuary, into which flowed a large river, subject to occa- 

 sional freshes charged with the testacea peculiar to its waters and the vege- 

 tation of the adjacent districts. 



In examining the various strata, we obtain in their lithological changes 

 some clue to the transporting power of the water by which the beds were 

 accumulated. As there is a remarkable difference in the range of organic 

 remains, attended also by corresponding but minor changes of lithological 

 structure between the northern and southern portions of the coal-field, it will 

 be necessary, in describing the mode of deposit of the measures, to refer as 

 nearly as possible to the central districts, where the principal phenomena of 

 north and south are co-existent. The reader must bear in mind, that in the 

 north of the coal-field at Donnington and Woombridge, the animal reliquite 

 exhibit their greatest variety ; that in proceeding south, they gradually de- 

 crease, the change commencing with those highest in the series; and that they 

 eventually disappear with the Penneystone stratum at Broseley (see Plate 

 XXXVII.) : certain general lithological characters, subject, however, to 

 considerable local variations, are co-extensive with these changes. When 

 reference is made to local phenomena, it is always mentioned. 



'&* 



Immediately succeeding the marine deposit of carboniferous limestone are thick irregular beds 

 of coarse sandstone, frequently passing into conglomerates, and containing a few impressions and 

 casts of imperfect fragments of vegetables. They graduate upwards into fine sandstones and 

 sometimes into shale. The crawstone, which occurs in one of these sandstones, contains numerous 

 beautiful casts of the Stigmaria fcoides, of which the internal structure is sometimes preserved, 



* The diagram of the coal-field, PI. XXXVII., exhibits proofs of these alternations. 



