A HISTORY OF BUCKINGHAMSHIRE 



At Brill there are chalky limestones and green glauconitic beds, 

 below which the pebbly layer is well seen overlying a few feet of brown 

 and greenish sand, which passes gradually down into the dark grey 

 Hartwell Clay, which again merges downwards into the Kimeridge 

 Clay. The clay is used for brickmaking, and in Roman times there 

 was a pottery at this locality. 



The Hartwell Clay which represents the Lower Portland Beds of 

 other localities contains Belemnites souicbi, Ammonites biplex^ Area longi- 

 punctata, Astarte hartwellensis, Tbracia tenera, Perna mytiloides^ etc. It 

 has been dug for brickmaking also at Whitchurch. 



At Long Crendon there are several exposures of the Portland Beds, 

 and in one pit near the southern windmill four formations were shown 

 in succession : 



Mr. A. Morley Davies estimates the thickness of the limestones 

 of the Portland Beds hereabouts at 32 feet, beneath which is about 

 2 feet of sand and the pebble bed with lydites, as near Aylesbury. Still 

 lower there is about 30 feet of light-coloured sandy beds with clayey 

 sands, and with a bright green sand at the base. These are the Lower 

 Portland Beds equivalent to the Hartwell Clay of Aylesbury and to the 

 Portland Sands in the south-west of England. 1 



The Upper Portland Beds of Buckinghamshire form dry brashy 

 soil, which is largely under arable cultivation. Springs are thrown at 

 the junction with the Hartwell Clay, and good supplies of water are 

 locally met with. At Dorton below Brill there is a famous chalybeate 

 spring. 



PURBECK BEDS 



Several of the more prominent of the outlying hills of Portland 

 Beds in the Vale of Aylesbury are capped by Purbeck strata, as at Oving 

 and Whitchurch, Quainton, Coney Hill, Brill and Long Crendon ; 

 other outlying patches occur at Haddenham and Cuddington, Stone and 

 Hartwell, and at Bishopstone, while their presence has been noted by 

 Mr. Morley Davies between Towersey and Kingsey, and by Fitton at 

 the Warren south of Stewkley, as well as at other localities. 



Of Purbeck as well as of Portland Beds we have but isolated 

 remnants of formations which may formerly have extended a good deal 

 further north ; but while the record of the Portland Beds is complete, 

 nowhere in this region have we the full thickness of Purbeck Beds. 

 They comprise a variable series of marls, compact and fissile limestones 

 known as ' Pendle,' and calcareous sands, with here and there a cherty 

 layer. The organic remains betoken their freshwater and estuarine 



1 See J. F. Blake, Proc. Geol. Aisoc. xiii. 74 ; and A. M. Davies, ibid. xvi. 21, 22. 



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