Geology of Coalhrook Dale. 461 



vilinear deposition of the mass. In the sand are frequently found angular frag- 

 ments of coal varying in size from a marble to blocks 5 or 6 feet in diameter; 

 and extensive accumulations of local gravel, of very variable thickness, are 

 generally exhibited in its lower part. I discovered no organic remains in this 

 deposit. 



On the hilly district south of the Severn the sand is not abundant, though 

 traces of it occur in Benthall and Posenal parishes ; but it has accumulated in 

 beds of considerable thickness in the valley of the Severn from Coalhrook 

 Dale, through Buildwas and Cressage, and thence westward, covering almost 

 everywhere the Wenlock shale and Caradoc rocks. In some places, it forms 

 small hillocks, as near Buildwas Abbey; at others, as atStrethilland Shineton, 

 it flanks, to the depth of several yards, the sides of the hills bordering the val- 

 ley. On the platform of the coal-measures it is again less abundant, and only in 

 patches, as at Lightmoor, where it is dug for the use of the iron furnaces. It 

 may be thence traced occasionally on the flanks of the hills and in the valleys 

 through Dawley and the Horsehays, increasing in importance as it ranges 

 northward, and extending over great part of New Lawley, New Dale, and 

 Ketley. In the latter place it much resembles the sands of the new red 

 sandstone, and is extensively excavated, for the moulds at the iron furnaces, 

 by the side of the high road immediately west of the Ketley works. It also 

 covers the surface rocks around Wellington, Hadley, and Woombridge ; like- 

 wise the low ground of Donnington, and the north of the coal-field. West- 

 ward of the Wrekin it appears very generally in the valley ranging parallel 

 to that mountain. 



The overlying deposit of gravel is of more general occurrence. It consists 

 of rolled pebbles of the adjoining Silurian and trap rocks, limestone, red sand- 

 stone, the shales, sandstone, &c. of the coal-measures ; also of a few small 

 boulders of granite, and schistose rocks. Fossils from the Wenlock shale 

 and limestone are extremely abundant in it at Madeley and on the south of the 

 Severn. In some parts of the valley on the eastern flank of the Wrekin, this 

 drift is imbedded in a tough, brownish clay derived apparently from the de- 

 gradation of the trap and other igneous rocks of the neighbourhood. 



Mr. Thursfield of Broseley discovered in the Willey gravel-pits a very 

 singular fossil. It was much water-worn, but displayed a chambered tube 

 inclosed in a sheath, to which it was attached by connecting septa. Prom its 

 mineralogical character, it had been probably derived from the Wenlock lime- 

 stone or shale. It possesses considerable similarity to the Orthoceratites from 

 the shores of Lake Huron, figured in one of the plates which accompanies 

 Dr. Bigsby's paper, in the Geological Transactions, 2nd Series, Vv I. I. 



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