84 THE ESSEX NATURALIST
creased, and was nearly two feet per annum, whilst from
1804 to 1844 it averaged 10 feet per annum. (Washington,
1853.) The village of Walton-le-Soken, with its church,
finally disappeared in 1796, and at Holland J. B. Redman
recorded that in 1863 '' the mere basements of the eastern
buttress of the church are left. (Redman, 1863.)
Measurements based on the 25" Ordnance Survey Plans
of different dates give further information. In the area one
third of a mile south of Walton Pier, where the cliffs are
70 feet high, a broad band 200-250 feet in width was lost to
the sea between 1874 and 1921, equivalent to an annual
loss of 4-5 feet. At the Naze, the recession has not been so
rapid, between 75 and 100 feet being eroded in the same
period. Further south, near Holland-on-Sea, where the
cliffs are lower and the London Clay is covered by a great
thickness of Glacial sand and gravel, the latter has facilitated
natural drainage and in consequence slumping has not been
so severe.
Many other instances of erosion could be quoted: all show
that continuous denudation has proceeded at variable rates
along the whole stretch of the coast where the London Clay
is the cliff-forming element. Attempts to arrest the erosion
by building groynes have been unsuccessful because the
authorities in the past failed to appreciate that sub-aerial
and not marine forces were mainly responsible. Adequate
protection can only be given if the slopes are artificially
drained and a promenade built at the cliff foot to prevent
undercutting which may take place during exceptional
storms. Protective measures on the above lines are at
present being carried out at Holland-on-Sea.
Man also has played a part in facilitating erosion by
exploiting the mineral resources of the London Clay. Iron
pyrites extracted from the cliffs at Walton at the rate of 150
tons a year during the last century greatly helped the re-
cession. The clayey limestone (cementstone) found in the
London Clay was also much sought after in the past for the
manufacture of Roman Cement. (Whitaker, 1887.) The
extraction of these two deposits may explain in part the
rapid increase in the rate of erosion in the first half of the
19th century given in Capt. Washington's report quoted
above.