212 MOUNDS NEAR THE ESTUARY OF THE THAMES.
The mounds at Sheppey are somewhat difficult of access; partly
for that reason, partly because they have been described in some
detail by others, I have devoted my examination chiefly to the
mounds of another area, where the main facts can be examined easily,
even in the course of a journey by train. That area lies right and
left of the London Chatham and Dover Railway, between Faversham
Station and Whitstable, where a fine and very characteristic exposure
of these mounds can be easily examined by travellers to and from
Whitstable, Heme Bay, and Margate. Two well-marked groups of
mounds occur here. The northernmost lies to the north-east of
Graveney Hill, in the alluvial tract between that hill and Whitstable
Flats. The other occurs in the same alluvial flat, right and left of
the railway between the third and fourth mile-posts from Faversham.
As this latter group is both the better developed and the more easily
examined, I have thought it better to take it as a type.
In regard to the geological structure of the district, the Geological
Survey Map (Sheet 3) shews a tract of alluvium, about two square
miles in area, shut in on the land side by low hills, which consist of
the lower part of the London Clay, together with part of the Lower
Eocene strata beneath it. These strata are inclined at a low angle,
nowhere more than three or four degrees, towards the north-east, and
their dip is continued to the south for several miles, so that the base
of the impermeable London Clay and the porous sands and pebble
beds at its base rise, from the sea level at Sea Salter, to elevations of
300 feet above that level about Dunkirk and the other hills to the
south of the locality under notice. The mounds at Sheppey are
situated in like manner in relation to the Eocene strata there.
Around Sea Salter the general form of the ground occupied by the
Tertiary strata does not call for any special remark, except that there
are certainly no traces of any marked and abrupt inequalities of the
surface anywhere discernable there. Their slopes incline gently
downwards, and finally disappear beneath the dead level of the
marshy alluvium in the usual manner. Here and there, projecting
through the alluvium, here, much as at Sheppey, are large mounds
that no one can reasonably regard as anything else than bosses of
London Clay, which the irregular denudation of the surface has acci-
dentally left at higher levels than the average level of the marsh floor
around. Associated with these mounds of natural origin are others
of smaller size, different mode of occurrence, and altogether charac-
terised by features of a distinct type. It is in regard to the nature