part 1] GAULT AND LOWER GREE]S^SA]S^D NEAll LEIGHTOIST. 37 



iron boxstone or streak of ' pan ' in the gritty beds at Grovebury 

 marks the taiUng-out of the locahzed conditions which produced 

 the iron-grit and its concomitants. These conditions, as will be 

 subsequently shown, were almost certainlj^ the existence, in a 

 current-swept sea, of a line of sand-banks, either awash or but 

 slightly submerged, which were indurated in places and scoured into 

 irregular reefs, with deeper water on the south. 



Brickyards in the Upper G-ault. — Before leaving the 

 Leighton sections, I will mention two brickyards in the up^^er 

 part of the Gault, on the Stanbridge road, nearly 2 miles south- 

 east of Leighton and rather over a mile east of the Grovebmy pits, 

 «.s reference will be made to them in the subsequent discussion, 

 although they are not otherwise relevant to the subject of this 

 paper. The pits, Faukner's on the south side of the road (see 

 map, fig. 1, p. 2), and Yirrell's on the north,i are in pale silty 

 marl}'^ clay of massive structure, unlike anything seen in the 

 sections around Leighton. Fossils are very rare, and I have found 

 nothing except impressions of ' Hamites ' and crushed indetermin- 

 able shell-fragments. The absence of ' Belemnites minimus,' so 

 plentiful in all unweathered sections around Leighton, is particu- 

 larly noteworthy. The pits are 20 to 25 feet deep, and were being 

 Avorked in 1920, but the greater part of the cuttings were then 

 slipped and obscure ; they were seen more clearly in 1912. 



Sections south-west of Leighton and beyond. 



Little is seen of the base of the Gault in the country east and 

 west of the big sand-pits of the Leighton distiict, partly because 

 of the prevalence of Glacial drift on the east and for 6 or 8 miles 

 on the west, and partly because of the inherent weakness of the 

 Gault, which rarely allows natural inland exposures. In three 

 places, however, excavated sections have been observed which prove 

 that the conditions characterizing the base of the Gault around 

 Leighton continue, at intervals if not unbrokenly, for 17 miles or 

 more south-westwards. [The first of these, discovered since this 

 paper was read, is an exposure in a small sandpit in the village of 

 Southcott, on the M^estern outskirts of Leighton Buzzard, about a 

 mile distant from the centre of the town.] The second was in a 

 brickyard at Littleworth near Wing, about 3 miles south-west of 

 Leighton ; the third, in an old brickyard and stone-pit at Long 

 Crendon in the Thame district, 17 miles south-west of Leighton. 

 In the two last-mentioned the Basement beds have overlapped the 

 Lower Cretaceous Sands, and rest directly on Upper Jurassic 

 strata. 



[Southcott (Buckinghamshire). — In this village, on the 

 Buckinghamshire side of the Ouzel valley, about a mile west of 

 the edge of my sketch-map (fig. 1, p. 2), a small sandpit has 



^ Yirrell's Pit lies just outside the eastern limit of the map. 



