Geology of Coalhrooh Dale. 467 



life — the increased transporting power of the water accumulating thick beds of sandstone, and 

 entombing large quantities of gigantic Sigillaria, Calamites, and Stigmaria. The vertical position 

 of a few of the larger specimens, with their roots attached, does not mar the supposition of their 

 having been transported, for the greater number of these fossils lie horizontally, or nearly so, 

 and at all levels. The gigantic character of this Flora, so different from that of the other 

 strata, appears to be a natural consequence of the long period of quiet during the accumulation 

 of the Penneystone measure — a period during which the vegetation of the country flourished vi- 

 gorously and uninterruptedly. May not part of the flint-coal which reposes upon this sandstone 

 have been derived from the woody matter of the large vegetable casts entombed in the rock ? 



The flint-coal lies upon this sandstone, and is, in the central and northern districts, covered by 

 a thin stratum of a very fine, dark, bituminous shale, containing a few scales and teeth of fishes, 

 and generally, in its upper part, a band full of crushed Unios, resulting probably from a suddenly 

 increased fluviatile action succeeding a period of calm. This is further confirmed by the inter- 

 polation between the shale and the white flat measure of a stratum of coarseish freestone or sand- 

 stone, occasionally conglomeratic, which commences at Ketley, and rapidly attains a thickness of 

 several yards, aflfording almost the first indication of a strong local action from the north-west- 

 ward, and forming a thick and irregular sedimentary deposit betwixt the regular and quiet accumu- 

 lation of the flint-coal bass and the white flat measure, which stratum thins out northward of 

 Ketley ; but to the southward of Ketley is in immediate superposition with the flint-coal bass. 

 It is in this portion of the coal-measures, that the important variations, both in the organic 

 remains and in the lithological structure of the northern and southern districts, begin to show 

 themselves distinctly. 



The white flat measure, which then succeeds, again brings us to a period, when conditions 

 prevailed somewhat similar to those under which the Penneystone measure was deposited. 

 Though the epoch was probably of shorter duration, yet we here find several new species of the 

 Trilobite family, and a large proportion of Unios and of plants, the more delicate parts of which 

 are well preserved, indicating, probably, a greater rapidity of accumulation than in the Penney- 

 stone ; whence the abundance of fluviatile, and the scarcity of marine Testacea. 



The system overlying this stratum consists of numerous alternations of rather thick coal-seams, 

 shale, and ironstone, and subordinate, fine-grained sandstones. The numerous remains of Sigil- 

 laria, Lepidodendra and other plants, generally associated with Unios, which occur sometimes, as 

 in the blue flats, in great quantities, — the frequency of the repetition of the different strata, and 

 their extensive and uniform persistence as far south as Lightmoor, appear to indicate many 

 changes and extensive but not powerful floods. 



Incumbent on the top coal, the highest in this last series, is a thin bed of fine bituminous shale, 

 which again proves the existence of the Megalichthys and other fishes, probably marine, whose de- 

 tached and scattered remains are preserved almost uninjured. 



Next follows a deposit, apparently of rapid but tranquil accumulation, forming the hailstone mea- 

 sure, a stratum characterised by the delicacy and beauty of its Flora, and by the absence of animal 

 reliquiae. The impressions of the leaves of the Cyclopteris, Neuropteris, &c., are so perfect, that 

 it is impossible to imagine the fronds could have been transported by violent currents, or that they 

 could have been long exposed to the action of the atmosphere and the water. The slightly 

 rumpled appearance of the delicate and unbroken tissue of the Cyclopteris orbicularis, the sharp- 

 ness and distinctness of every fibre of the Neuropteris gigantea, and other plants, could only have 

 resulted from an immediate and tranquil entombment. 

 VOL. v.— SECOND SERIES. 3 P 



