72 REPORT—1850. 
exactly in composition with those of the present beach, and which, from their thick- 
ness, must have been accumulated about the level of low water. 
We have thus presented on a vertical section (Fig. A):— in 
Ist. Zone (d) composed of division (a) covered with Fucus vesiculosus, and divi- 
sion (4) above the former, and extending to the upper limit of the present tides, or 
the actual tidal zone. 
2nd. Zone 2, which represents the upper portion of a former tidal zone when the 
coast was at a lower level, and when the sea reached the base of the cliff B. 
3rd. The still lower level indicated by the marine beds at the base of cliff, (which 
underlie the accumulations (X) and the marginal), and the upper limit of which is 
to be found at some distance from the present coast line, at D. 
I do not propose to offer any relative geological dates for the accumulation X, nor 
for a bed containing marine pebbles on its upper surface, nor yet for the underlying 
beds at C,D. The most recent change is obviously that indicated by zone 2, a 
movement of no great amount (8 to 10 feet), but of which we find evidences where- 
ever the nature of the coast admits of it. A depression of the land of such like 
amount would convert many of the present river-valleys of the south of England into @ 
estuaries. The valley of the Exe, much to the east of the spots whence the forego- 
ing observations have been made, as also that of the Ouse on the Sussex coast (vide 
Mantell), present mud-beds with modern estuary shells, at slight elevations above the 
present sea-level ; these and such deposits I would refer to zone No. 2 on the line 
of section here described, as a first step towards disentangling the very complicated 
phenomena which the younger accumulations seem to present ; and should this be 
correct, we may infer that the latest change of level was extended to the whole 
length of our channel with a like amount of effect. 
| 
On the constant Increase of Elevation of the Beds of Rivers. 
By Dr. Lupwic BEcKER. 
Assuming as acknowledged facts frequently observed, that the older buildings in 
towns situated on the banks of rivers appear as if they had partially sunk into the 
ground, the germs of churches, the basements of the gates of towns, of towers, of an- 
cient walls, all giving evidence of this kind, while old pavements, and steps down 
from quays are no longer visible, the author endeavours to account for these phz- 
nomena. Choosing’ Mayence, from its ancient importance, and its situation on one 
of the greatest of rivers, the Rhine, he shows the depth of ground which has been | 
accumulated in layers, by the destruction of human habitations in Roman, Medizval, 
and modern times. In one case, three layers, six feet each, occurred in the centre of 
Mayence. Close to the river banks, and forming a portion of the city walls, is the 
Fish-gate, which was built in 1050. 
1, Excavations lately made by the side of this gate, brought to light the covered 
street-pavement of the time of 1050, and with it the basements, or, architecturally, 
the socle of the stone gate-pillars themselves. The pavement thus discovered was very 
nearly six feet deeper (5°9) than where the carriages travel in the present day. 
2. On repairing the river quay in the vicinity of this gate, the workmen got down 
to two distinct layers or strata of road-paving, one two andea-half feet, and one six 
feet below the level of the present causeway. 
