MIDDLE CHALK—WILTSHIRE, 
451 
Shalbourn inlier. From the gap above mentioned, near the village 
of Marten, the basset surface runs westward in a narrow band along 
the north border of the Vale of Pewsey as far as Arn Hill. 
Near that spot the northerly dip becomes less steep, and this division 
occupies more space, partly in the form of three outlying tracts. 
North of the valley of the Kennett it spreads out over the broad 
area of the Marlborough Downs, but is covered here and there by 
outliers of Upper Chalk and of clay with flints. From Ogbourne 
St. George it occupies an irregular space around the inkers and 
inlets of Lower Chalk near Liddington Warren, Wanborough Plain, 
and Bishopstone Down. 
The component parts of the Middle Chalk in Wiltshire are similar 
to those of the same stage in the adjoining counties of Dorset and 
Hampshire. The Melbourn Rock has its usual character of a hard, 
nodular, chalky limestone from 5 to 10 feet thick, and its outcrop 
generally forms a feature which can be easily traced across the 
country. This is succeeded by less hard nodular chalk passing up 
into firm-bedded chalk, and the higher beds (Terebratulina zone) 
consist of massive white chalk, firm rather than soft, in the upper 
part of which there are generally two or three layers of black flints. 
The thickness of the Middle Chalk appears to increase both north¬ 
wards and eastwards. A boring at Lower Pert wood Farm, near 
Monkton Deverill, between the Vales of Wardour and Warminster, 
proved it to be there only 80 feet thick, and this seems to be its 
thickness along the northern border of the Vale of Wardour. At 
Warminster and Westbury it is about 90 feet, but eastward along 
the southern border of the Vale of Pewsey it thickens till at the 
eastern end it is from 140 to 150 feet. North of Devizes it thickens 
in the same way from 100 to about 140 feet west of Swindon. 
Fossils are not abundant in the Middle Chalk of Wilts, and very 
few were found either by Mr. Bennett or myself during our mapping 
of the areas described, but it is probable that most of the usual species 
would be obtained from some of the quarries if the workmen were 
employed to look for them. The most notable exposures will now 
be mentioned, commencing in the most southern part of the county. 
Stratigraphical Details. 
In the Vale of Broad Chalk, many exposures of Middle Chalk 
can be found, but, according to my colleague, Mr. F. J. Bennett, 
there are few large quarries in it. He saw the Melbourn Rock at 
Broad Chalk at the top of a quarry north of Chalk-pit House, and 
again in the road south of Knighton. 
I visited Homington and Combe Bisset in 1890 ; south of Hom- 
ington I found a quarry in the zone of Rh. Guvieri showing : 
feet. 
Hard chalk, broken and weathered, with two layers of greenish 
marl. Inoc. mytiloides - - 6 
Hard whitish nodular limestone - seen for 6 
4219., G G 
