160 



T. E. LONES — GKAVELS, SANDS, CLAYS, 



Hughes, are generally regarded as being older than the Briclcet 

 Wood boulder-clay, and younger than the pebble-gravel already 

 described. 



The beds of gravel and sand vary very greatly in thickness, even 

 in different parts of the same area, and they almost always rest 

 upon a very uneven surface of the Upper Chalk, or upon clay-with- 

 flints of variable thickness which covers the Chalk. In several 

 places near Vicarage Road, Watford, the beds are as much as 

 30 feet thick ; at Brightwells a thickness of about 9 feet is shown ; 

 and near Bushey Hall the beds are about 15 feet thick. 



The mineral composition of the beds is so varied, and to a large 

 extent characteristic, that a somewhat detailed description of it will 

 be given. For this purpose, it will be convenient to imagine a large 

 quantity of the gravels and sands of average composition to be 

 gi'aded or sorted into three lots, and then to describe these lots 

 separately, beginning with the coarsest. In this way let the 

 gravels and sands be graded by means of two rings, whose diameters 

 are six inches and three-sixteenths of an inch respectively. The 

 coarsest of these portions forms a comparatively small fraction of 

 the whole, and is mainly composed of large unworn flints and blocks 

 of greywether sandstone and Hertfordshire pudding-stone. Some 

 of the blocks of greywether sandstone are very large, and one about 

 4 feet long is exposed in a gravel-pit near Yicarage Road, Watford. 



Section 7. — Gravel Pit, Watford. 



A A. Soil. 



B B. Flint gravel. 



C C. Browu loam, with pebLIes. 



E D. Manganese beds. 



E. Gravel with large flints and quartzite pebbles. 



F F. Light-brown sand. 



G G. Gravel with large flints and quartzite pebbles. 

 II. Brown sand. 



The second portion of the graded material consists chiefly of 

 angular and subangular flints, flint-pebbles, quaiiz-pebbles, pieces 

 of coarse sandstone or grit, and well-rounded pebbles of brown, 

 reddish - grey, red, purplish - red, and nearly black quartzite. 

 Occasionally specimens of chalcedony, sandstone (])robably from 

 the Lower Greensand) with a large quantity of limonite as 



