at Beaconsfield and Penn, between Chalfont St. Giles and Amersham, and to the east of Chesham. [1]
Many of these outliers form picturesque wooded tracts, diversified with commons, as at Lane End and Cadmore End Commons, where the strata are evidently faulted. In some dark sands at this locality traces of nickel and cobalt have been detected.[2]
The most distant outlier is that noticed by Mr. Whitaker at Ring- sail to the north of Ashridge Park and not far from the Ivinghoe hills, where a pit showed fine white sand. In such situations relics of Eocene strata are preserved in deep pipes in the Chalk, far away from the parent source, as the mass of the strata above had been removed by erosion. [3]
The mottled clays are dug in many places for brickmaking, the sands for mortar making, and the pebble beds for road mending. Both sands and pebble beds yield a fair amount of water under favourable circumstances.
LONDON CLAY
This great clay formation forms the substratum over much of south-eastern Buckinghamshire, but like the Reading Beds it is almost wholly concealed by gravels.
It has been observed at the surface at Upton and along the borders of Stoke and Fulmer Commons, at Iver, and to the east and north-east of Fulmer. Outliers appear at Lane End, Penn and Tyler's Hill east of Chesham. In many places the clay is dug for brickmaking.
Nowhere in the county have we the full thickness of the formation, but the greatest thickness is probably on the borders of the Colne, south- east of Wraysbury. In mass it is a bluish-grey clay with septaria, brown at the surface. The basement bed, 6 or 8 feet thick, is a brown loam, which contains flint pebbles and green sand. The sand is sometimes cemented into tabular masses of rock, and these are in places crowded with fossils, such as Cardium, Cytherea, Panopaea, Pectunculus, Nucula, Natica, Rostellaria and Ditrupa plana. Many have been found at Hedgerley.
Fossils are by no means common in the mass of the London Clay. We may occasionally meet with a Nautilus, but near the surface the shells have been almost wholly destroyed. The fauna and flora are of tropical aspect.
There is a great gap between the London Clay and succeeding deposits in Buckinghamshire. Of the interval we have no actual records in the county. The Bagshot Beds were no doubt spread over large areas, for they occur in Middlesex and on the Berkshire and Surrey side of the Thames valley. During Oligocene, Miocene and Pliocene times the area must have undergone great waste by subaërial agents. The London Basin took form by the upraising of the bordering
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