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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 comfortably 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] ——

Upper Portland Beds	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Earthy and shelly limestones	about 10 feet
		Sands	" 5 "
		Rubbly limestone with many fossils	" 8 "
		Sands with Conglomerate at base yielding many pebbels of lydite	" 10 "
Lower Portland Beds		Hartwell Clay	upwards of 20 feet

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 portlandica, 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. Soc. ser. 2, iv. 279-92 ; and J. F. Blake, Quart. Joun. 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, Ædes Hartweliana (1851-64).

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