450 
THE CRETACEOUS ROCKS OF BRITAIN. 
CHAPTER XXXV. 
THE MIDDLE CHALK IN WILTSHIRE. 
General Description. 
The course of the Middle Chalk through Wiltshire is very 
irregular, because of the anticlinal flexures which bring up the 
underlying beds in the Vales of Broad Chalk, Wardourl War¬ 
minster and Pewsey, so that the boundary lines run for long 
distances in an east to west direction. The width of surface 
occupied by the Middle Chalk in this county also varies greatly, 
for where the dip is slight it runs far up the numerous valleys 
which cut through the chalk hills, while where the dip is high 
the space so occupied is but a narrow strip of ground. 
From above Charlton near Shaftesbury the outcrop runs east¬ 
ward and surrounds the several irregular inkers of Lower Chalk 
which occur in the Vale of Broad Chalk. This vale is separated 
from that of Wardour by a long and narrow ridge of chalk, the 
upper part of which is capped by the beds which overlie the Chalk 
Rock. This ridge terminates westward in the promontory which 
is called White Sheet Hill, and the northern slope of the ridge forms 
a tine escarpment ending eastward in a great curve which is known 
as Hoop Side (see Map in Vol, I., Plate opp. p. 248). 
On the north side of the Vale of Wardour the outcrop is very 
narrow, owing to the high dips, and in several places it is cut out 
altogether by the fault which runs along this tract. From 
Mere it passes northward to the valley of the Deverill and up on to 
Brimsdown Hill, near Maiden Bradley; thence eastward to the 
valley of the Wily, along which it is exposed as far as Staple ford. 
It forms the upper slopes of the hills east of Heytesbury and 
Warminster, and an outlying patch of it forms Clev Hill, three miles 
west of Warminster. 
From West bury, north of Warminster, the main outcrop of the 
Middle Chalk runs eastward along the escarpment to Lavington 
and thence still eastward along the southern side of the Vale of 
Pewsey. There are, however, numerous inkers in the deep valleys 
which trench the chalk of Salisbury Plain south of the main escarp¬ 
ment, and inlets from the outer tract run southward up the valley 
which breaches the escarpment ridge at Lavington and also down 
the valleys of the Avon and the Collingbourn. 
At the eastern end of the Vale of Pewsey the outcrop of the Middle 
Chalk opens through a gap in the watershed ridge, and thus becomes 
continuous with the cincture of Middle Chalk that surrounds the 
