Geology of Coalbrook Dale. 469 



from the peculiar lithological character, and the preponderance of large and 

 aged corals in the carboniferous limestone, conjointly with its gradual thinning 

 off in its range southward, indicating its accumulation in a tranquil and rather 

 shallow sea, undisturbed by the immediate influx of any large river, yet evi- 

 dently receiving, as the sea became deeper to the northward, a large supply 

 of fine silt, perhaps from the northward — it is probable that the change con- 

 sisted of a subsidence along the south-west shores of the sea in which the 

 lower carboniferous limestone was accumulating; for had the movement 

 been elevatory, a portion of the bed of the ocean, and consequently of the 

 carboniferous limestone, must have been exposed, and outliers of that forma- 

 tion would most probably have existed at a distance from the coal-measures, 

 which now, on the contrary, overlap its edges. Again, we could not expect 

 to find in the detritus derived from land recently elevated from the bottom of 

 the sea, remains of land plants ;"whereas these remains are extremely common, 

 and we even find a thin and irregular bed of coal at the very base of the mea- 

 sures. We may consequently infer, that an extensive area experienced a con- 

 siderable subsidence, depressing one portion beneath the sea, and materially 

 modifying the physical geography of the remaining dry land, giving rise both 

 to a new line of coast and to a new system of drainage, enlarging some rivers 

 and forming others. No sooner, indeed, do we pass into the coal-measures, 

 than we find, throughout their entire vertical range, evidences of strong river 

 action in the presence of transported vegetables, of which the majority are, 

 according to A. Brongniart, such as might be expected to have flourished on 

 low and marshy lands ; and fluviatile shells, intermingled with the marine Tes- 

 tacea of the sea into which they were drifted. From these great mutations 

 would probably result — at first, barren conglomerates and coarse sandstones, 

 succeeded by strata produced by a more fixed and settled order, as the effects 

 of the preceding paroxysms were gradually softened down and effaced. Vege- 

 tation, it may be inferred, flourished on the land, and Testacea and fishes mul- 

 tiplied in the sea, during those intervals of disturbance arising from inunda- 

 tions and freshes of the river, which flowed probably from the south-westward, 

 carrying its detritus into a sea, where the dispersion of it was apparently 

 limited by a current from the northward. 



While on this subject, a few remarks may be made on the debris forming 

 he coal-measures, and on the origin of the ironstone. The fine-grained 

 quartzose sandstones — the constantly recurring pebbles of white quartz — 

 the general diff'usion of mica, and occasionally of felspar and slate rocks, 

 evidently denote an origin in the older stratified formations; whilst the red 



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