Dr. PiTTON on the Strata below the Chalk. 271 



by mining in the lower ground on the north-east of that place, between Rumbold Copse and 

 Whitehouse Farm. Tlie formation is much less distinct at Tetsworth, but is obvious on the south 

 of that village ; in the descent of the hill from Chinnor towards Emington; and beneath the lower 

 Icknield-way, at Chadwell Hill on the north-west of Risborough ; at North Lee, between Tur- 

 wick and Bishopstone ; and probably in the vicinity of Aston-Clinton. On the north of Tot- 

 ternhoe, great quantities of a soft variety of firestone were formerly obtained from mines of 

 ancient date deeply seated at the foot of the lower-chalk escarpment, between the village and 

 the hill on which is the mound of ancient encampment, called Maiden's Bower. In this latter 

 direction, also, an outlying portion of the Upper green-sand is visible, on the road between Kate's 

 Hill and the Turnpike near the beginning of HocklifFe, forming the base of an outlier, or penin- 

 sular portion of clialk, which shoots oif from the main body about Chalton, and bears upon it 

 the village of Wingfield ; — not improbably crossing the road and forming part of a flat-topped 

 range of heights, which extends westward on the north of Tilsworth and Stanbridge. 



Gault. — The gault in this part of the country is very irregularly diffused, in many places forming 

 a distinct valley or depression beneath the Upper green-sand, in others spreading itself towards 

 the west, and thinning off gradually over the top of the Lower green-sand. 



Lower green-sand. — This formation, which is indistinctly seen in the lower ground, is best 

 observable near the summit of the heights between Garsington and Shotover on the south-west of 

 Oxford (No. 18.), — and of the corresponding ranges, from Long Crendon to Brill (No. 19.), and 

 from Quainton to Whitchurch, on the north-west of Aylesbury (No. 20. & X. b. fig. 11.) Thence 

 towards Leighton Buzzard, the Lower green-sand is more obscurely seen : but it becomes con- 

 spicuous in approacliing Woburn, and is found in immediate apposition with the Kimmeridge 

 clay, at Little Brick Hill (No. 21'.), where the whole of the intermediate strata, from the 

 Wealden to the Portland sand, are wanting, — having been either originally deficient, or partially 

 carried away before the deposition of the sand. 



The greatest extent of continuous surface which this formation occupies here, is between 

 Leighton* and the west of Woburn. But there can be little doubt that it once extended con- 

 tinuously from its rise beneath the gault to its final outcrop in the heights above mentioned ; 

 the greater part having been subsequently removed by denudation. 



On the main road from Tetsworth to Wheatley, Section No. 18'., a portion of the gault and 

 of this sand still remains between the 44th and 47th milestones ; while on the south-west of the 

 road, a great part of these strata having been removed, the surface is so much lowered as to 

 disclose the subjacent Portland stone, throughout a space which includes the villages of Great 

 and Little Milton and Great Hazeley. 



Several outliers of the Lower green-sand in this part of England still remain to be examined; 

 among which the heights near Faringdon seem to be especially deserving of notice. Another 

 detached portion (which, if the chalk range had been unbroken by the chasm of the Thames, 

 would have been nearly at the same distance from the escarpment as that of Faringdon), caps the 

 hills at Bagley Wood and Cumnor, on the south and south-west of Oxford. These have been 

 generally described by Mr. Conybeare (Outlines, p. 190.), who states that the Portland beds do 

 not extend so far : but as the relations of the Wealden group were unknown at the time of his 



* A large tract around Leighton, including Wing, Cublington, Aston Abbots, Mentmore, &c., 

 has not yet been described geologically. The late Mr. Bevan of Leighton was thoroughly 

 acquainted with it ; and I am not without hope that some of his obsexvations may be published 

 by his son. 



VOL. IV. SECOND SERIES. 2 N 



