'32 MR. Cr. Av. LAMPLLGH ON THE jrxcTiox OF [vol. Ixxviii, 



drift. A clismaDtlecl brickyard on the Stanbridge Eoad, near the 

 Leighton AVaterworks, was worked in the lower part of the Gault, 

 and may at one time have revealed the junction, but showed no 

 section when I examined it in 1912. The Avell-boring at the 

 AVaterworks, 150 yards farther east, is recorded^ to have passed 

 through: — Gravel, 10 feet; Blue Clay, 32| feet; Dead Sand, 9^ feet; 

 Blowing Eed Sand & pebbles, 3| feet — continuing in the Lower 

 Green sand to a depth of 111: feet. 



The range of workings at Grovebury, under different proprietors, 

 extends east and west for over half a mile, and usually disj^lays in 

 one part or another magnificent exposm-es of the cross-bedded 

 Leighton Sands. Though similar in general structure and size of 

 grain, the sands of these sections differ from the Silver Sands north 

 of Leighton in colour and mineralogical character, not having the 

 same high silica value, and therefore not being adapted for the 

 purposes requiring that quality. Many of their well-rounded 

 highly-polished grains are coffee-coloured, or rusty, or nearly 

 black,- and these are often arranged in streaks which bring out 

 the current-bedding beautifully. They are also frequently mottled 

 with tubular ' worm-markings," accentuated in the same way by 

 the assortment of coloured grains ; and some curious V-shaped 

 structures in the mass are similarlj^ outlined. The difference 

 appears to be original, though it may possibly be due to some 

 process of bleaching and ferric segregation in the Silver-Sand area, 

 as suggested by Prof. P. G. H. Boswell.'^ It is noteworthy in this 

 connexion that the development of hard iron-grit masses and iron- 

 pan is rarely seen, except among the Silver Sands. 



Owing to the low level of the Grovebury pits, the saturation- 

 limit or water-table of the Ouzel valley is reached in all the deeper 

 excaA'ations. This has led to the adoption of a method of quarrying 

 the Sands by steam-dredgers or diggers afloat on the pool formed 

 in the floor of the pit, the sands being thus extracted to 20 feet or 

 more below water-level. 



It was mentioned in our paper of 1903 (o/y. cit. p. 239) that the 

 junction of the Sands with the Gault had been nearly reached in 

 the Grovebury pits ; and the anticipation was realized in 1904, 

 when I found that the Spinney pit (see map, fig. 1, p. 2), at that 

 time the easternmost of the range — now worked out and filled with 

 a deep water-pool, showed the following section : — 



1 '"Water Supply of Bedfordshire & XortliamptorLsliire ' Mem. Gaol. Sta-v. 

 1909, p. 54. 



- I am indebted to Sir Jethro Teall for the folloTring note on these coloured 

 gTains : — ' The glossy brown grains . . . are bro"UTL throughout, and Tvhen 

 boiled in hydrochloric acid become nearly white. They are not reduced in 

 ?ize, and after treatment appear to consist of chalcedonic silica. The solution 

 contains much ferric oxide " {in lift.. August 14th. 1920). 



'^ ' On British Eesoui'ces of Sands suitable for Glass-making, &c.' London. 

 1916, p. 66. 



