Geological Society/. 383 



stem ; 3rdly, the old red sandstone ; Jthly, carboniferous limestone; 

 5thly, coal measures ; 6thly, new red sandstone j and, 7thly, trap. 



In describing the formations subjacent to the old red sandstone, 

 Mr. Prestvvich states that he owes his knowledge of their order of su- 

 perposition entirely to the previous labours of Mr. Murchison, and 

 that unassisted by them it would have been impossible for him to have 

 determined correctly their relative antiquity. 



1 St. The lower Silurian rocks consist of quartzose grit succeeded by 

 micaceous flags, which are overlaid by a coarse-grained sandstone 

 alternating with beds of light grey clay. They occur on the flanks of 

 the Wrekin and Arcol Hills. 



2ndly. The Wenlock rocks are composed, in the lower part, of beds 

 of shale, and in the upper of limestone abounding with organic re- 

 mains. They form the escarpment of Wenlock and Benthall Edges, 

 Lincoln Hill, &c. The Ludlow rocks consist of three divisions: the 

 lowest being formed of grey-coloured, soft, calcareous sandstones 

 and shales ; the middle of very thin beds of light grey and brown 

 limestone; and uppermost of sandstones. They are stated to occur 

 at Much Wenlock and Wyke, also near Apley, in the Meadow-pits 

 and in several other pits in Broseley parish ; likewise between Dean 

 and Willey, &c. 



3rdly. The old red sandstone skirts the southern parts of the coal- 

 field, and consists of beds of dark red marl alternating with dark, mi- 

 caceous sandstones. 



4thly. The carboniferous limestone appears on the south of Little 

 Wenlock, at Steeraways and Lilleshall Hills, and presents thin beds 

 of argillaceous limestone and shale. 



5thly. The coal measures consist of the usual alternations of shale, 

 sandstone, and coal, amounting at the Madeley Meadow pits to 135 

 beds, having an aggregate thickness of about 250 yards. The first 

 70 or 80 beds are light grey, yellow, or red ; the succeeding 20 are 

 nearly black, and the underlying are mostly light-coloured. These 

 distinctions are general, but not universal. In the uppermost part of 

 the series clays and soft calcareous sandstones predominate ; in the 

 middle argillaceous sandstones and indurated clay ; while in the lowest 

 part fine hard sandstones. The upper coal seams are thin, generally 

 sulphurous, widely separated, and extremely irregular, but the lower 

 are nearer together, and are persistent throughout the field. The 

 average thickness of the seams is about 3 feet, and the number in 

 diff"erent pits varies from 1 to 16. The following table contains the 

 aggregate thickness of the seams and the number at each of the loca- 

 lities mentioned : 



Yards, ft. in. Number of beds. 



Hadley 15 16 



Sned's Hill 14 2 2 12 



Malmslee II 10 13 



Langley II 2 6 U 



Dawlev 14 16 



Lightmoor 13 2 17 



Madeley 10 2 10 24 



Broseley 7 9 13 



