ST. ALBANS AND ITS NEIGHBOURHOOD. 
215 
country from the north, extending so far south as the London 
Clay hills on the borders of Middlesex and Hertfordshire. 
Before the Glacial Period, however, a bed of gravel was 
deposited on the London Clay, the “ gravel of the upper plain ” 
of Prof. Hughes, the Westleton Shingle of Sir Joseph Prestwich. 
It occurs on the Tertiary outlier on Bernard’s Heath, and on the 
London Clay at Shenley and elsewhere, but nowhere directly on 
the Chalk, which seems to show that the erosion of the Tertiaries 
from the surface of the Chalk had not taken place when this 
marine pebble-gravel was deposited. 
The Glacial deposits consist of gravel and sand overlain in 
places by boulder-clay, but sometimes, as west and south of 
Wheathampstead, boulder-clay rests immediately upon the 
Chalk. The gravel is mostly of sub-angular flints from the 
Chalk with fragments or boulders of “foreign rocks,” or rocks 
derived from a distance, and there is much chalk in its 
composition, both in large masses and small fragments. The 
Devil’s Dyke and the Moat, south of Wheathampstead, are cut 
through boulder-clay; No-Man’s-Land Common is on gravel 
mapped by the Geological Survey as glacial, and the village 
of Sandridge is on the same, but its church is on boulder-clay; 
there is much boulder-clay about midway between St. Albans 
and Hatfield, overlying gravel and sand; and the most south¬ 
westerly patch known is that on which Bricket Wood is situated. 
In gravel believed to pass under it there the tooth and tusk 
of an elephant have been found, but the stratigraphical position 
of the gravel is somewhat uncertain. 
A great part of St. Albans is situated upon glacial gravel; 
it is worked in the large gravel-pits of Sopwell; according 
to the map of the Geological Survey that part of the dry 
valley to be mentioned later which extends from south of 
Harpenden nearly to the Colne at Colney Heath is in it, 
though it has more the appearance of a river-gravel; its largest 
spread in our area shown on that map is from there to Colney 
Street, but this also appears to be fluviatile. 
St. Albans is also partly situated immediately on the Chalk, 
without any superficial deposit but surface-soil; most of the 
ancient city of Verulam was so placed; but there is on the 
Chalk in part of the city, and on part of the site of Verulam, 
a deposit, usually thin, called clay-with-flints. This is a stiff 
brown or reddish clay with large unworn flints. It was formed, 
and may still be forming, by dissolution of carbonate of lime, of 
which the Chalk chiefly consists, its aluminous matter being 
left as a matrix for the indestructible flints, and possibly some 
waste of the Tertiary clays formerly covering the Chalk enters 
into its composition. There is much clay-with-flints about 
Childwick and south of Redbourn, and the whole of Gorhambury 
Park is on it. 
Another superficial deposit to be mentioned is brick-earth, 
which is a mixture of clay and sand forming a loam much 
