434 J. Prestwich, Esq., on the 



very slightly S.S.W. From that locality, it extends almost to the Frog Mill 

 near Coalmoor. This division is marked by a great paucity of organic re- 

 mains; a Lingula and an Avicula being, though of rare occurrence, the 

 characteristic fossils. 



The formation is traversed by two sets of joints, the one ranging from N. 

 12° E. and S. 12° W. and the other W.S.W. and E.N.E. nearly. 



The limited development of the Ludlow rocks in the district under exa- 

 mination, precludes an extensive list of the organic remains ; and although 

 the different divisions are well marked throughout, by the presence of several 

 characteristic fossils, yet a great number of those, which Mr. Murchison de- 

 scribes as abounding further to the south, are here wanting. 



THE OLD RED SANDSTONE. 

 (PI. XXXV. and XXXVI., figs. 1, 12, 13, 14, and 16.) 

 This formation skirts the southern parts of the coal-field, reposing on the 

 Ludlow rocks, and occasionally underlying the coal-measures. Along the 

 edges of the former, to the S.E. of Much Wenlock, it consists of a very dark 

 red clay, alternating with rather hard, dark red, speckled, or gray micaceous 

 and fissile sandstones, and with thin beds of a gray, micaceous marl. In the 

 red sandstone (dipping 12° S.E.) at Wenlock Walton, I found casts of the 

 Lingula cornea, a characteristic fossil of the tilestone, or lowest division of 

 the old red sandstone. In the lane to the southward of, and just below Bar- 

 row, the same beds are nearly horizontal, but I found no fossils. The old 

 red sandstone here occupies a low tract, about one-third of a mile broad, in- 

 sulating the outlier of coal measures on Shalot Hill. It then ranges around 

 the base of Willey Hill and Linley Hill to Holly Bush, where a narrow tongue 

 of it stretches eastward into the coal-measures. From the last locality, it may 

 be traced, underlying the coal measures which cap the hills from Nordley, to 

 Tasley. Dark red clays and marls predominate throughout the district, but 

 they contain subordinate beds of coarse, highly micaceous, gray and red sand- 

 stones. The strata to the south and west are so covered with drift, that they 

 can rarely be seen. It thus appears, that the old red sandstone reaches no 

 further north than Barrow and Willey; and that at this extreme point, the 

 lower division or the tilestones of Mr. Murchison, is moderately developed 

 only in the western side, and that the spotted argillaceous marls and deep red 

 clays, with their subordinate beds of sandstone, occupy the greater portion of 

 the district forming the base of Shirlot Hill. 



CARBONIFEROUS LIMESTONE. 

 (PI. XXXV. and XXX VL, figs. 1 to 7, 13, and 14.) 



In the south of the field, the coal-measures have been shown to repose upon 



