Mr. Lonsdale on the Oolitic District of Bath. 269 



lington, Heddington, Dunkirk, the Canal Locks near Devizes, Drews Pond, 

 Eastvvell, Crockwood Mill, the side of the hill near Lavington Lodge, the brick- 

 yard between Dues Water and Great Cheverell, Coulston, Bratton, Eden 

 Vale near Westbury, and Westbury Leigh, and may therefore be inferred to 

 constitute a band ranging at the foot of the Chalk Hills. 



Upper Green Sand. 



' This formation is composed of siliceous sand, containing beds and nodules 

 of calcareous sandstone and chert. 



The sand is generally of a very fine grain, the particles being for the 

 greater part not distinctly visible to the unassisted eye; but it is sometimes, 

 though rarely, of a coarser texture. The colour varies from light grey to dark 

 green, and is occasionally of different shades of yellow. No permanent order 

 is visible in the arrangement of the colours, but in some districts (Earl Stoke, 

 Coulston, Urchfont,) the dark green occupies the upper part of the formation, 

 the grey the middle, and the yellow the bottom. The sand seldom possesses 

 any great degree of compactness; but, from the presence of argillaceous matter, 

 it becomes sometimes a friable sandstone. 



The calcareous sandstones are likewise principally of a fine grain; occa- 

 sionally, however, they pass into quartzose conglomerates ; and from certain 

 portions being tinged with oxide of iron, they not unfrequently assume 

 the characters of a breccia. The calcareous cement often appears in distinct 

 crystals, and gives the rock a glistening aspect. The colour varies from light 

 grey to dark green and yellow. The hardness of the sandstone is sometimes 

 considerable, but at others it is trifling. Blocks are occasionally found, of 

 which organic remains constitute the greater part. 



In the lower portion of the formation near its junction with the gait, small 

 patches or streaks of blue clay are frequently visible. 



Spangles of mica are generally diflused through the sand and sandstones. 



Chert occurs abundantly in the neighbourhood of Warminster ; but in the 

 district to which this memoir in particular belongs, it appears to be entirely 

 wanting. 



The upper green-sand forms a narrow band ranging along the foot of the 

 Chalk Hills from Cherhill by Calstone Willington, and Heddington to 

 Roundaway. At New Park near Devizes, commences a narrow plain belong- 

 ing to this formation, and extends by Wick Green to Pottern, and thence to 

 Sleight Farm, Stert, Urchfont, Market Lavington, and Little and Great Che- 

 verell to Earl Stoke, where the superficial dimensions again contract to another 

 narrowband, which may be traced by Tinhead, Edington, Bratton, Westbury, 



