GEOLOGY 



Discina latissima. In Buckinghamshire the upper beds pass into some- 

 what sandy grey clay, well adapted for brickmaking, and dug for the 

 purpose at Brill and Whitchurch. These beds indeed merge into Lower 

 Portland strata, and they contain numerous iridescent fossils, including 

 Ammonites biplex (see p. 10). 



PORTLAND BEDS 



Resting conformably upon the Kimeridge Clay are the Portland 

 Beds, which appear from beneath the great covering of Cretaceous strata 

 at Haddenham and Cuddington, Dinton and Hartwell. It may be that 

 the portions here exposed are but parts of a large outlier, as we have 

 no evidence of their occurrence underground far to the south. North- 

 wards we find a group of outliers wholly or in part formed of Portland 

 Beds as at Long Crendon, Brill and Muswell Hill, Ashendon, Nether 

 and Over Winchendon, Quainton, Oving and Whitchurch, Weedon 

 and Aylesbury ; while an inlying mass appears beneath the Gault 

 between Cublington and Wing. 1 



The general characters of the strata may be best observed in the 

 sections in the neighbourhood of Aylesbury, where the succession is as 

 follows : 2 



The upper beds of limestone have been quarried for building stone 

 and lime at the Bugle Pit, Hartwell. Large ammonites known as 

 Ammonites giganteus and A. boloniensis, Natica ceres, Cardium dissimile, 

 Pecten lamellosus, Lucina portlandica, Ostrea expansa and species of Perna 

 and Trigonia occur. Examples of the large ammonites, which are 

 sometimes 3 feet in diameter, were built in the walls bounding Hartwell 

 Park by the former proprietor, Dr. John Lee. 3 



The lower rubbly limestones, known as Aylesbury stone, occur at 

 Aylesbury and yield Myoconcha portlandka^ Umcardium^ and many fossils 

 which occur in the higher beds. The pebbly layer has been exposed 

 at Bierton and in a brickyard where the Hartwell Clay is worked between 

 Aylesbury and Hartwell. It is in some places cemented into a hard 

 rock. 



1 See Fitton, Trans. Geol. Sac. ser. 2, iv. 279-92 ; and J. F. Blake, Quart. Joum. Geol. Soc. 

 xxxvi. 215. 



2 W. H. Hudleston, Prof. Geol. dssoc. x. 166 ; and H. B. Woodward, 'Middle and Upper Oolitic 

 Rocks of Britain,' p. 225. 



3 See Admiral W. H. Smyth, JEdes HartwelRana (1851-64). 



I 9 2 



