548 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 8, 
Solent has become an arm of the sea by the severance of the Isle of 
Wight from the mainland. 
(e) The last movement appears, however, to have been one of sub- 
sidence. Submerged forests have been observed in Poole Harbour, 
off Bournemouth, off Southsea Castle, off Pagham, and at Ports- 
mouth. Sir Charles Lyell* adopts the conclusion of the Bishop of 
Gibraltar, that the Bournemouth forest was submerged by the wash- 
ing out of a sandy substratum without a general subsidence of the 
land, and explains the occurrence of the similar deposits on the 
north side of Poole Harbour in the same manner. The section at 
Portsmouth, which was described by Sir H. James t, appears, how- 
ever, to afford good evidence of a downward movement. An old ter- 
restrial surface with rooted trees which, when living, must have stood 
at least 30 feet higher, was exposed in the dockyard in 1847, and 
has been again brought to ight, but at a higher level, in the works 
for the extension of the dockyard now in progress. The origin of 
Poole Harbour and Christchurch Harbour, and of Portsmouth, 
Langston, and Chichester Harbours, is probably in a great measure 
due to this subsidence, which, according to Mr. Godwin-Austen ¢, 
there is some reason to believe has gone on till within the last few 
centuries. 
(f) The denudation which the surface of the country has under- 
gone since the deposition of the gravel on the plains is as remarkable 
for its partial character as for its extent. Large areas of the plains 
at the highest levels appear to have remained quite unchanged, while 
close by deep valleys have been scooped out, and high escarpments 
have been formed by what cannot have been any other than sub- 
aérial causes, and while large tracts of land have been gradually 
removed by the action of the sea on the neighbouring coast-line. 
The nature of the geological formation appears to have had no 
part in influencing the destruction or the preservation of the surface. 
Barton Clay, Bagshot Sand, and Headon Marls alike underle the 
gravel of the New-Forest tableland, and have alike been removed 
over the area drained by the tributarics of the Boldre river, of which 
Lyndhurst isthe centre. The gravel covering itself is probably the 
protective agent, and it may have been thinner or more loamy where 
the old surface has been destroyed. 
VY. SUMMARY. 
The chief points to which attention has been called in the fore- 
going paper are as follows:— 
1. That the gravel plains of the New Forest and the neighbour- 
hood are portions of a tableland rising slightly to. the northward 
and attaining an elevation of 420 feet: and that the remains of 
similar tablelands exist on the east side of Southampton Water, 
* Principles of Geology, vol. ii. p. 580. 
+ Quart. Journ. Geol. Soe. vol. iii. p. 249. 
~ Quart. Journ. Geol. Soc. vol. vii. p. 118. 
