By G. Poulett Scrope, Esq., MP. 103 
generally full of coral, and thence called Coral rag, compose a range 
of low hills that stretch across the whole county, ina N.E. and S.W. 
direction from Westbury through Steeple Ashton, Rowde, Calne, 
Lyneham, and the Lydiards, to Highworth. This range is crossed 
by the Great Western Railway at Wootton Bassett, through the 
same depression as the Wilts and Berks Canal. In many parts it 
preserves still the aspect and structure of a marine Coral reef; 
which it no doubt once was. The Corals belong chiefly to the 
genera Thecosmilia, (fig. 13). Protoseris, and Thamnastrea. The 
Ostrea gregarea, (fig. 14,) is also very characteristic of this portion 
of the oolitic series in England as well as on the continent. So 
also is the Cidaris coronata, (fig. 15). 
Fig. 13 (354). 
CON 
bs 
Thecosmilia annularis, Milne ¢ Oise 
Edw. and J. Haime. Ostrea gregarea. Cidaris coronata. 
Coral Rag, Steeple Ashton. Coral rag, Steeple Ashton Coral rag. 
This range of coralline oolite separates the vale of Oxford clay 
from a corresponding vale composed likewise chiefly of clay, gene- 
rally dark coloured and bituminous or peaty, called by Smith 
Oak-Tree or Kimmeridge clay, from a place of that name in Dorset- 
shire where it is prevalent. In our county it occupies a nearly 
continuous depression parallel on the east to the coral rag range 
just described, and lying between it and the escarpment of the chalk, 
from Westbury to Rowde, and again after an interruption of six or 
seven miles, from Calne by Highway to Swindon and Shrivenham. 
At Swindon, and again in the Vale of Wardour, and also near 
Potterne, this clay is overlaid by strata of sand and limestone, 
