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Rh Chalk tracts and the removal from the higher grounds of great masses of Eocene strata. The relics of this denudation have mostly been worked up into the Drifts which were deposited at various periods during Pleistocene and recent times, but it is possible that some of the irregular accumulations known as Clay-with-flints may date back to the Miocene and Pliocene periods.

On the higher Chalk tracts, especially about Chesham, Little Missenden, Little Hampden and High Wycombe, there are thin but widespread accumulations of unworn, little worn and broken chalk flints and reddish-brown clay. On some ploughed fields there appears to be such a mass of these flints that it is difficult to believe that any crop could be grown, yet turnips and other roots flourish.

When we see a cutting through this accumulation of Clay-with- flints we find the Chalk to be irregularly eroded in great hollows or ' pipes,' some of which may be 50 feet deep and 20 feet or more across. These hollows are due to the dissolution of the Chalk, and the dark brown Clay-with-flints which lines these pipes and occurs as a thin covering on the irregular surface of the Chalk is the residue. Some, if not all, of these pipes may be regarded as swallet holes, formed on the margin of Eocene Clay areas, before the Eocene strata were wasted away.

In practice we have to include with the Clay-with-flints a very variable accumulation. Preserved in some of the pipes and sometimes intermixed with the Clay-with-flints are relics of Reading Beds, such as mottled clays and sands and pebble beds ; and thus since some of the pipes were formed there is evidence to prove that the Tertiary strata have been so eroded that only small outliers, or the contents of pipes, remain here and there.

Large areas of loam or brickearth, much of it bright and mottled in colour owing to its derivation from the mottled clays of the Reading Beds, occur on the higher Chalk tracts at St. Leonards, Lee and Hyde Heath east of Great Missenden, again to the south of Hampden, on Priestwood Common and Wycombe Heath, on Bledlow Ridge, on the hills above Bradenham, on Radnage Common and near Lane End.

Numerous unworn flints occur in the loam, also irregular masses of greywether, a hard sandstone, almost a quartzite, of which materials have been extensively dug, broken up and squared for paving at Aylesbury and other places.

Professor Morris mentioned that blocks of the stone known as Hampden Stone have been extracted 5 or 6 feet in length, and used as ornamental stones or rude pillars as at Hartwell Park. Masses of Hertfordshire puddingstone also occur. This is but a pebbly modification of the local greywethers, which are indurated masses of sands