Geology of Coalbrook Dale. 447 



vegetable impressions are common, and they occur, though more rarely, in the 

 body of the same strata. It has been already observed, that, in some rare in- 

 stances, traces of the original vegetable tissue remain. In one of the black bitu- 

 minous shales, associated with the yard-coal, are found impressions of Perns, 

 marked by a thin, bright coating of iron pyrites. The fossil plants in the sand- 

 stone strata are almost invariably casts in the matrix, the bark being frequently 

 converted into coal. The principal specimens which retain the internal organ- 

 ization belong to Stigmaria Jicoides , and were found in the Crawstone ; the 

 stem of a large coniferous tree was also found in the flint-coal. The former of 

 these fossils is figured and described in the Fossil Flora (Plate 166. fig. land 2.) . 



The distribution of the organic remains is extremely irregular in different 

 parts of the coal-field ; but the fossils of the lower series, like the strata them- 

 selves, are persistent throughout a much greater area than those of the upper. 

 Thus, the Stigmaria jicoides and the Neuroptera gigantea are found as 

 abundantly at Broseley as at Hadley. The Penneystone measure has been 

 shown to be characterized, at different localities, by the preponderance of pe- 

 culiar fossils. The sandstone above this measure contains but few plants at 

 Broseley, and they are principally Stigmariae ; whilst at Ketley, Calamites, 

 Sigillariae, and Lepidodendra, are abundant. The gregarious nature of tlie 

 Trilobite family is evinced by their congregating within very small limits, for 

 they have becH found only in the White Flat, at one pit in Ketley, except a 

 species of Asaphus, which exists in the Penneystone. 



The numberless Unios which characterize the centre of the coal-measures 

 at the Horsehays, Malinslee, Ketley, Woombridge.. &c., are rarely met with 

 at Broseley and Madeley. The ballstone, with its numerous and beautiful 

 vegetable fossils, is not known much further south than Ketley ; and the 

 Chance Penneystone, so full of the Leptcena scabricula, is entirely confined to 

 the northern districts of the coal-field ; whilst the Microcnnchus carbonarius 

 and Cj/pris inflata have not been detected to the north of the Severn. 



NEW RED SANDSTONE. 



(Plates XXXV. and XXXVI., figs. 1 to 16.) 



This important and extensive formation wraps around the two longer sides 

 of the acute-angled triangle in which the foregoing series are developed ; its 

 disjointed edges abutting, as already mentioned, against those of the several 

 older deposits. 



Mr. Murchison* has shown, that the new red system, in its range through 

 Cheshire, Shropshire, Staffordshire, and Worcestershire, consists of the fol- 



* Proceedings Geol. Soc, Vol. II., p. 563, Feb. 1835. Geol, Trans., ante p. 31. 



