SUBSIDENCE OF EASTERN ENGLAND.
97
movement. It may be briefly rehearsed here. Freshwater
shell-marl and peat occur in the Orwell below Ipswich, 14 feet
beneath low-water level. Submerged forests, with tree-stools in
position of growth, are found at Dovercourt and Clacton. The
foreshore at Walton is a freshwater alluvium, down to at least
low-water mark. Granaries and other buildings at Colchester
Hythe, not three centuries old, are frequently flooded now.
The foundations of the old Roman town of Othona exist at the
extreme edge of low-water of spring-tides, more than a mile
from the shore at St. Peter's Chapel, Bradwell-on-Sea.
The 30 inches per century suggested above would be amply
sufficient to admit of the Thames having been fordable at
Tilbury during the Roman occupation. I must decline archaeo-
logical controversy as to the historic veracity of the supposed
passage, on which its present impossibility has been regarded
as a conclusive negative argument; but it harmonises with the
less ancient record of the limpid and fish-inhabited rapids
under London Bridge, then 60 yards seaward of the existing
erection.
I lately happened on a paper published in 1891 by E. Van den
Broeck1 entitled "Subsidence of France: Geological Evidence
for Col. Goulier."2 The author shows that the very precise
levellings in 1857-1863 and 1884-1890 demonstrated elevation in
progress south of a stationary axis between Montpellier and
Marseilles, and subsidence northward of that axis. "There is
[he says] a well-marked sinuous valley of depression from
Narbonne, by Valence, Lyons, Dijon, Troyes, Chalons-sur-
Marne, and Amiens to Lille, where the total depression
amounted to .78 m. The annual subsidence is less about Dijon,
greater north-eastward of Paris." It is suggested that the
secular contraction of the globe is bringing the crystalline
massifs of Brittany and the Ardennes into a narrower space, in
which movement the trough of softer rocks in the interval is
being deepened by the approach of its flanks. As the Brittany
massif probably extends, though concealed, through the
Midlands, by Bletchley and Orton, to Leicestershire, the Pennine
Range, and Scotland, and as the Ardennes may be regarded as a
southern outlier of Scandinavia, the North Sea and its adjacent
1 Bulletin de la Societe Belge de Geologie (t. v, pp. 13-21).
2 See article by Col. C. M. Goulier, Patria Belgica, t. i, pp. 49-51, 1873. G