_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 _debris_ 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 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.