Heordshire | Page 3

is laminated, and has at its
base the Melbourn Rock and at its summit the Chalk Rock. Nodules of
flint, greenish in appearance, and (rarely) arranged in layers, occur
sparsely in the Middle Chalk, which may be traced in the
neighbourhood of Boxmoor, Berkhampstead and Baldock, and also in a
few other districts.
The Upper Chalk.--Although, as has been stated, the configuration of
Hertfordshire is very undulating, we are able to discern a general trend
in certain districts. Thus, there is a gradual slope to the S. from the N.W.
and central hills, a slope which comprises the larger part of the county.
This slope is formed of the Upper Chalk, a formation abounding in
layers of black flints. The chalk is whiter than that of the lower beds,
and very much softer. Fossil sponges, sea-urchins, etc., are abundant in
this formation.
TERTIARY.--Many of the chalk hills of Hertfordshire are strewn with
outlying more recent deposits which prove that the lower Tertiary beds
were more extensive in remote ages. The beds of sand and clay, of such
frequent occurrence in the S.E. districts, contain fossils so distinct from
those of the Upper Chalk that an immense interval must have elapsed
before those Tertiary deposits were in turn laid down.
The Eocene Formation.--The Thanet Beds, of light-coloured sands,
present in some other parts of the London Basin, notably in Kent, are
wanting in Hertfordshire. There are, however, some widespread
deposits of loamy sands which may possibly be rearranged material
from the Thanet Beds.
The lowest Eocene deposits in the county are the Reading Beds. These
rest directly upon the Chalk and have an average thickness of, say, 25
feet. They may be traced E. to S.W. from the brickfields near Hertford
to Hatfield Park; thence to the kilns on Watford Heath and at Bushey;
they may also be traced from Watford to Harefield Park. These beds
contain flints, usually found close to the Chalk, and consist chiefly of

mottled clays, sands, and pebble-beds. Fossils are but rarely found.
From the Woolwich and Reading Beds come those conglomerate
masses of flint pebbles commonly called Hertfordshire plum-pudding
stone. These have usually a silicious matrix and were often used by the
Romans and others for making querns for corn-grinding. It is, perhaps,
not impertinent to mention here the opinion of geologists that during
the Eocene Period a considerable portion of the land usually spoken of
as S.E. England was covered by the ocean.
Resting upon the Reading Beds we find that well-known stratum called
the London Clay, which is of bluish hue when dug at any considerable
depth. It is found in some of the same districts as the Woolwich and
Reading Beds, and from Hertford and Watford it extends to N.E. and
S.W. respectively until it leaves Hertfordshire. Its direction may be
approximately traced by a series of hills, none of which are of any great
height.
The Drift.--In Hertfordshire, as elsewhere, the strata whose names are
so familiar to geologists do not form the existing surface of the ground.
For the origin of this we go back to a comparatively recent period,
when disintegration was busily working upon the solid rocks, and
glaciers were moving southwards, leaving stones and much loose
débris in their wake. Rivers, some of which, as in the Harpenden valley,
have long ceased to run, separated the flints from the chalk, forming a
gravel which is found in quantities at Harpenden, Wheathampstead and
St. Albans, and is, indeed, present in all valley-bottoms, even where no
river now runs. Gravel, together with clays, sand, and alluvial loams,
forms, for the most part, the actual surface of the county.
The Rivers of Hertfordshire are many, if we include several so small as
hardly to deserve the name. They are the Ash, Beane, Bulbourne, Chess,
Colne, Gade, Hiz, Ivel, Lea, Maran, Purwell, Quin, Rhee, Rib, Stort
and Ver.
1. The Ash rises near Little Hadham, and, passing the village of
Widford, joins the Lea at Stanstead.
2. The Beane, rising in the parish of Cottered, runs to Walkern, where it

passes close to the church, and flows from thence past Aston and
Watton, and into the Lea at Hertford.
3. The Bulbourne rises in the parish of Tring, passes N.E. of
Berkhampstead and S.W. of Hemel Hempstead and unites with the
Gade at Two Waters.
4. The Chess enters the county from Buckinghamshire at Sarratt Mill,
and flowing past Loudwater joins the Gade at Rickmansworth. The
Valley of the Chess is one of the prettiest districts in the shire.
[Illustration: ON THE RIVER COLNE]
5. The Colne rises near Sleap's Hyde, is crossed by the main road from
Barnet to St. Albans at London Colney, and by the main road from
Edgware to St. Albans at Colney Street. Thence it passes between
Bushey