Geology of Coalbrook Dale. 419 



axis, from near Watling Street to Leighton and Shineton, and thence south- 

 ward. The dip varies considerably, either conforming to the flanks of the 

 numerous masses of trap, or to that of ihe subjacent grits and schistose flags. 

 This rock is well characterized by its organic remains, which are numerous 

 in the bands of limestone; the most common being- the Pentamerus lavis, 

 Orthis alternaf.a &nd Tentaculites annulatus, with several Crinoideaand corals. 

 Mr. Murchison mentions many new species of Pentamerus, Nucula, Orthis, 

 and Trilobites, as characteristic of the deposit in other districts*. 



UPPER SILURIAN ROCKS. 

 The Wenlock Shale. (Pi. XXXV. and XXXVL, figs. 8 to il, is, ii. and 15.) 



In the neighbourhood of Leighton Hurst and Morel's Wood the Caradoc 

 sandstone disappears under a calcareous shale, belonging to this formation. 



It is well and extensively developed, and rises from below the Wenlock lime- 

 stone, which constitutes the upper part of the escarpment of Wenlock Edge, 

 Benthall Edge, and Lincoln Hill. Tlie shale, in each instance, forms the base 

 of the range, and extends across the valley of the Severn to the escarpment of 

 the coal measures, below which it disappears. Good sections of it are exposed 

 along the banks of most of the brooks by which it is intersected, and on the 

 sides of the Severn, at Buildwas. It is uniformly a thin, laminated, calcareo- 

 argillaceous shale, sometimes finely micaceous, and it occasionally contains 

 nodules, and a few thin, subordinate beds of impure limestone. Its colour 

 varies from light greenish gray to light liver. It is tenacious and adhesive 

 when wet ; but when dry, it splits into imperfectly rhomboidal masses, having 

 an earthy fracture. It has been proved to extend as far north as Lightmoor, 

 where, at a depth of eighty yards, and underlying the coal-measures, Mr. 

 Thompson met with a calcareous shale, which, by its fossils, I recognised as 

 the Wenlock shale. Its organic remains are numerous and beautifully pre- 

 served. Among the most characteristic in the neighbourhood of Coalbrook 

 Dale are, Asaphus caudatus, common in groups in the upper part of this 

 formation, Orthis iestudmaria, (Sow.), Orthoceras annulatum, (Sow.), and 

 Terebratulce, with a few crinoidea and corals. 



The Wenlock Limestone. (Pi. XXXV. and XXXVL, figs. 9 to U.) 



The Wenlock shale passes gradually upwards into the Wenlock limestone, 



which presents a steep escarpment over the vale formed of the shale. The 



limestone ranges through the district in a narrow belt from Lincoln Hill to 



Much Wenlock, and thence in a south-westerly direction into Wales, South- 



* Silurian System, p. 704, et seq, 

 VOL. V. SECOND SERIES. 3 I 



