WESTLETON BEDS TO THOSE OF NORFOLK, ETC. 139 



very few in number, and gradually become rarer as we proceed 

 northwards, although in a few instances they extend to the edge of 

 the Chalk Downs. 



At Collier's End (348 feet) and Sacombe Green (362 feet), five 

 miles north of Ware, are two small Lower Tertiary outliers with a 

 thin capping of quartzose shingle (Westleton). Others lie on some 

 of those near Welwyn, — on Ayot (406 feet) and Burnham Green 

 (407 feet) hills. 



North of St. Albans, and between the valleys of the Lea and the 

 Gade, traces of Lower Tertiary strata may be found as far north as 

 Eerkhampstcad Common, but they are rarely in sufficient force to 

 be worked, or high enough to bring in the Westleton Beds. At 

 Bennett's End, near Hemel Hempstead, the Tertiary strata are 

 capped at a height of 456 feet by a bed of sandy clay with a thin 

 uneven patch of Westleton gravel, consisting in large proportion 

 of flint- and quartz-pebbles with a few subangular flints (not stained), 

 fragments of Lydian stone, and a few flat ovate light-coloured quartz- 

 ite-pebbles. The bed varies from 1 to 6 feet in thickness, and rests 

 on from 30 to 40 feet of London Clay and Lower Tertiary strata. 



There is another Tertiary outlier at Little Heath and Potten, 

 extending to Berkhampstead Common, or rather it is a mass of 

 Tertiary strata preserved in a depression in the Chalk, of great 

 extent. There is some appearance of Westleton Shingle, but too 

 indistinct for description. 



The hills to the west of the Gade present similar features. The 

 Tertiary Beds are, however, so mixed up with Glacial debris that 

 they are to be recognized only in a few instances. At Laugley 

 Common (440 feet) there are traces of Westleton Shingle, and closely 

 adjacent to the borders of Hertfordshire is the more conspicuous 

 outlier of Tiler's Hill. 



South Buckinghcmisliire. — In this county, as in Hertfordshire, 

 the picturesque high ground of the Chilterns is covered by a 

 sprinkling of Glacial Drifts (but no Boulder-clay), and " Ked Clay 

 with Flints," with occasional Tertiary remnants. 



Tiler's hill*, 2 miles east of Cheshara, rises to a comparatively 

 considerable height above the surroundiiig Chalk-plateau, and 

 consists of Lower Tertiary strata with an outlier of London Clayt. 

 On the summit, about GOO feet above the sea-level, is a small 

 capping of gravel, composed of: — 



per cent. 



1. Tertiary flint-pebbles, small and large, many of them 



weathered white 55 



2. "White quartz-pebbles 23 



3. Very subangular fragments ol' flint, stained yellow ; others are 



large, white and little worn 12 



4. Chert &c 5 



5. Flat ovate pebbles of light-coloured quartzite and veinstone, 



with subangular fragments of Tertiary sandstone and pudding- 

 stone 5 



100 



* On the new one-inch map this name is altered to Crowcroft. 



t Described by the author in Quart. Journ. Geol. Soe. vol x. p. 90 (1854), 



