Hertfordshire. Herbert W. Tompkins
words. The predominant formations are the Cretaceous and the Tertiary.
Cretaceous.—Ignoring the Gault, which barely touches the county, this formation consists chiefly of Chalk-marl, Lower, Middle and Upper Chalk. A series of Chalk Downs, an extension of the Chiltern Hills, stretches, roughly speaking, from Tring to Royston, forming by far the most prominent natural feature of Hertfordshire. The oldest rocks are in the N.W.
The Chalk Marl is superimposed upon the Gault and Upper Greensand beds, which are confined to the western portion of the county. Its upper layer passes into a sandy limestone, known as Totternhoe stone, which has furnished materials for many churches in the shire. Ashwell, Pirton and Tring may be named as neighbourhoods where this stratum may be traced.
The Lower Chalk is devoid of flints, and rests, in somewhat steeply sloping beds, upon the Totternhoe stone. It forms the western slopes of the Dunstable Downs, and of the Chiltern Hills. It is fossiliferous, one of the commonest of its shells being the Terebratula.
The Middle Chalk, of resonant hardness, 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.
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 Hall and Bushey Lodge, flows through Watford to Rickmansworth where, uniting with the Gade and Chess, it enters Middlesex near Stocker’s Farm.
6. The Gade rises near Little Gaddesden, skirts Hemel Hempstead Church on the W. side, and passing King’s Langley and Hunton Bridge, flows through Cassiobury Park and joins the Chess and Colne at Rickmansworth.
7. The Hiz, rising at Well Head, S.W. of Hitchin, crosses that town, joins the Purwell at Grove Mill and leaves the county at Cadwell.
8. The Ivel rises near Baldock, flows to Radwell Mill and shortly afterwards enters Bedfordshire.
9. The Lea is the largest river in Hertfordshire. It rises near Leagrave (in Bedfordshire) and flows through the county from N.W. to S.E. Entering Hertfordshire at Hide Mill, it flows past Wheathampstead, Hatfield, Hertford, Ware, and, leaving the county near Waltham Abbey, enters the Thames at Blackwall. Its entire length is about 50 miles. The waterway known as the Lea and Stort Navigation is navigable to Bishop’s Stortford.
10. The Maran, or Mimram, rises in the parish of King’s Walden, skirts Whitwell on the N., running parallel with the village street, and passing through Welwyn and near Tewin enters the Lea at Hertingfordbury.
11. The Purwell, or Pirall, rises in the parish of Ippollits and passing W. of Great Wymondley runs to Purwell Mill, and joins the Hiz at Grove Mill.
12. The Quin rises in the neighbourhood of Wyddial, and passing Quinbury, unites with the Rib at Braughing.
13. The Rhee, rising a little E. of Ashwell, has but a few miles to flow before it enters Cambridgeshire.
14. The Rib rises at Corney Bury, flows E. of Buntingford, thence turning W. it flows under the bridge at the Adam and Eve, runs to Westmill, Standon and Thundridge, finally uniting with the Lea at Hertford.
15. The Stort enters Hertfordshire from Essex at a point near Cannon Wood Mill, and after passing through Bishop’s Stortford forms the extreme E. boundary of the county for some distance before quitting it near Cheshunt.
16. The Ver rises near Flamstead, is crossed by the Dunstable Road, N.W. of Redbourn, then recrossed by it. It then skirts St. Albans on the S. and joins the Colne near Park Street.
In addition to the cutting of the Lea and Stort Navigation already