260 Mr. Lonsdale on the Oolitic District of Bath. 



tremely irregular. The western boundary has been ah'eady given in detaihng 

 the extent of the forest marble. The eastern defines a waving outline, from 

 the nei"-hbourhood of Kington St. Michael, by Chippenham, to Laycock. At 

 that village the two boundaries merge into one ; and the cornbrash forms a 

 narrow band by Shut-in-Lane, Wick Farm, and Whitley, to Atford, where 

 it acquires a greater importance ; and the eastern boundary may be traced 

 from the foot of Atford Common, by Linton Farm, Great Chalfield, Holt and 

 Widbook, to Midway. At this point the formation again contracts into another 

 band, which passes along the western extremity of Winfield Common to 

 Vagg's Hill, Langham Mill, and Rowde. From that village the cornbrash 

 takes an eastern direction, and circles around the elevated ridge of forest 

 marble, which extends from Beckington to Cutteridge, passing through 

 Mark's Lane, Lamber's Marsh, Southwick, Pole's Hole, Cutteridge-House- 

 Farm, Lower Ridge, and Standervvick Court, and thence to Clink and Stile's 

 Hill. 



In addition to these continuous districts, the cornbrash appears on the sum- 

 mit of Pipe-House-Hill near Midford, and at Wick Farm near Farleigh. It 

 likewise forms a narrow strip extending from the neighbourhood of Upper 

 Studley, by Trowbridge and Hilperton, to Semington, and an outlier around 

 Chatley House, Woolverton, and Lullington. 



Oxford Clai/. 



The Oxford clay is seldom laid open in Wiltshire. On the surface it ap- 

 pears invariably as a stiff, pale blue or yellowish clay, which effervesces 

 vividly with acids. At the junction with the Kellovvay rock, a bed occurs of 

 a pale lead colour streaked with yellow ; and in some parts of the formation 

 strata are found of a chocolate hue, and thinly laminated structure. 



Near the bottom of the Oxford clay is a bed of calcareous sandstone, from 

 three to five feet thick, and abounding with organic remains : it is usually 

 known by the name of the Kelloway rock. The fossils are occasionally so 

 numerous as to constitute nearly the whole of the stratum, but are often want- 

 ing; and the stone then agrees in character with the calcareous grit interposed 

 between the Oxford clay and the coral rag. The usual colour of the rock is 

 brown on the surface, but blue or grey in the interior. 



The accompanying section was procured from the quarry at Christian 

 Malford. 



Pale lead. coloured clay, streaked with yellow. 



Rotten, ruhbly stone, highly charged with oxide of iron, and in- 

 closing few organic remains 5 feet. 



