wanting in Hertfordshire. There are, however, some widespread deposits
of loamy sands which may possibly be rearranged material from the Thanet
Beds.

The lowest Eocene deposits in the county are the _Reading Beds_. These
rest directly upon the Chalk and have an average thickness of, say, 25
feet. They may be traced E. to S.W. from the brickfields near Hertford
to Hatfield Park; thence to the kilns on Watford Heath and at Bushey;
they may also be traced from Watford to Harefield Park. These beds
contain flints, usually found close to the Chalk, and consist chiefly of
mottled clays, sands, and pebble-beds. Fossils are but rarely found.
From the Woolwich and Reading Beds come those conglomerate masses of
flint pebbles commonly called Hertfordshire _plum-pudding stone_. These
have usually a silicious matrix and were often used by the Romans and
others for making querns for corn-grinding. It is, perhaps, not
impertinent to mention here the opinion of geologists that during the
_Eocene Period_ a considerable portion of the land usually spoken of as
S.E. England was covered by the ocean.

Resting upon the _Reading Beds_ we find that well-known stratum called
the _London Clay_, which is of bluish hue when dug at any considerable
depth. It is found in some of the same districts as the _Woolwich_ and
_Reading Beds_, and from Hertford and Watford it extends to N.E. and
S.W. respectively until it leaves Hertfordshire. Its direction may be
approximately traced by a series of hills, none of which are of any
great height.

_The Drift._--In Hertfordshire, as elsewhere, the strata whose names are
so familiar to geologists do not form the existing _surface_ of the
ground. For the origin of this we go back to a comparatively recent