Part of Gloucestershire and Somersetshire. 34:3 



§ 21. In the northern portion of the field, the limestone is uninterrupted 

 by other beds ; but on approaching the plain it alternates with sandstone, of 

 which the first bed that appears is forty fathoms in thickness. I have traced it 

 around the basin, from West-End near Wickwar on the east, into the Tyther- 

 ington ridge on the west ; and in the whole of this course its position is con- 

 formable to that of the limestone in which it is included. The same may be 

 said of two or three other beds of sandstone, from I to 2^ feet thick, which 

 succeed the bed last mentioned, and are interstratified with the limestone. 

 These may be followed from the Tytherington ridge into the dell north of 

 Cromhall church ; and analogous beds are occasionally exposed to observation 

 on the eastern side of the basin. These beds of sandstone are generally of a 

 grayish or yellowish white colour, seldom tinged with red, and are composed 

 of granular quartz, with incidental scales of mica, and, rarely also, grains of 

 felspar. 



§ 22. The carboniferous limestone of this district is in general of a blueish 

 gray colour, of various degrees of intensity, sometimes verging toward black ; 

 occasionally also, when adjacent to sandstone, of a reddish hue. Its structure 

 is commonly compact, also conjointly compact and foliated, very rarely granu- 

 larly foliated. It is not unfrequently fetid. When contiguous to sandstone, 

 a reciprocal incorporation often ensues, the latter being penetrated with car- 

 bonate of hme, and the former with sandy particles. This is particularly 

 observable in the vicinity of the forty fathom bed of sandstone, where the 

 limestone, on either side, is, in the first place, intermixed with visible grains 

 of sand; but at some distance from the line of contact, the limestone, both 

 above and below the sandstone, acquires the oolitic structure, which it retains 

 throughout the range from Tytherington to Wickwar. It would seem as if 

 the proximate cause of this disposition were minute particles of sand; a 

 progression being traceable from the granular sandy, to the perfect oolite lime- 

 stone. The upper and lower beds of this description do not appear to possess 

 a determinate thickness ; the inferior strata sometimes consisting of nests, or 

 clusters, of oolite limestone, enveloped in the compact. The oolitic structure 

 is most distinct in the eastern quarter, but in the northern and western por- 

 tions of the range, the grains are in general so minute, that the stone at first 

 sight appears to be compact. The continuous limestone is, not unfrequently. 



observed on the banks of the Bristol Avon, where the limestone strata dip in general to the south 

 20° east, at angles varying from 20*^ to 40". In this limestone, a bed of bituminous coaly shale, 

 varying from a few inches to one foot in thickness, has been lately discovered near the Hot Wells. 

 VOL. VI. 2 Y 



