Richmond Park is on this stratum, and Woodward frequently refers to this place in his History of Fossils; but there are no longer any sections to be seen there, the spot being covered by buildings.
Wells of 70 feet deep have been dug at Harrow-on-the-hill; and several in London between 200 and 300 feet deep. At other places on rising grounds the depth of this stratum is much greater. In digging a well for Lord Spencer, at Wimbledon, they were obliged to go 530 feet deep before they got through it to the sand which contained water. At Primrose-hill, near Hampstead, a well was dug some years ago to the depth of 500 feet without success.
This considerable formation may not only be traced on the north side of Kent and Surrey, but almost the whole counties of Middlesex and Essex are composed of it. At South-end, and Leigh in Essex, there are good sections of it. But not having an opportunity of visiting the coast farther to the north, I am unable to speak with certainty respecting the various strata to be observed there.
The cliffs at Walton and Harwich, in Essex, have been best described. From various accounts the lowest part consists of blue clay, the fossils of which agree generally with those of Hordwell, Sheppey, &c. This clay is covered by deep beds of gravel, sand and marl, containing not only great quantities of fossil shells but also the remains of land animals.
From the confused manner in which these shells and pebbles lie, as described by Mr. Dale in his history of Harwich, there can be no doubt but that the strata containing them are frequently alluvial; though in the cases where he describes them as lying in patches of particular genera, we may suppose that portions of the original strata remain undisturbed.
Many of these latter fossil shells must belong to some of our latest strata: they are described as scarcely mineralized, very friable, and of a dead white colour.