66 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



An old terrestrial surface of the same age and level as that of 

 Portsmouth Harbour is to be seen at extreme low-water to the east 

 of Southsea Castle, passing beneath the sea. On the land-side it is 

 overlaid by a thick accumidation of mud, sand, and shingle, part of 

 which is now permanently raised above the level of high-water ; 

 there has therefore been a rise at this place subsequent to the 

 original depression : the lower mud-deposit of the harbour-section 

 represents a condition of the estuary such as exists at present ; and 

 the presence of the intermediate shingle-band is an indication of a 

 greater amount of depression, just as a slight subsidence now would 

 cause the shingle of Stokes Bay to be spread out over the present 

 mud-flats of the harbour. 



3. Isle of Wight. — At the north-eastern end of the Isle of Wight 

 the latest movement also appears to have been one of depression. 

 There is abundant evidence that rather more than a century ago 

 there existed a line of broad mud-flats in advance of the shore, such 

 as those on either side of Lymington Creek, above described : this 

 fact is noticed by Sir H. Englefield. 



When Fielding was at Ryde, on his voyage to Lisbon in 1 753, he 

 describes it as totally inaccessible by sea, except at or near high 

 water, as the tide left a vast extent of mud too soft to bear the 

 lightest weight. This mud-bank is now entirely covered by a stratum 

 of fine sand, smooth and firm enough to bear wheel-carriages. This 

 bed of sand now extends from Xettlestone Point, as far as Binstead, 

 having covered two miles of shore during the last half century ; and 

 the inhabitants say that it is still extending to the westward. 



These sands are many feet in thickness on the east of Ryde, and 

 I ascertained that they everywhere overhe the former mud-bank. 

 The sands are bare at low water, but not to a greater extent than 

 were the former mud-banks : there must therefore have been a sub- 

 sidence along this part of the coast of very recent date ; and, if we 

 may judge from the increasing thickness of the sands from west to 

 east, the depression has been greatest in that direction. 



An attempt was made some time since to reclaim Brading Har- 

 bour, an area of considerable extent at the eastern end of the Isle of 

 Wight, and much of which is left dry at low water. The sea was 

 shut out, and in the course of the works for the drainage of the tract, 

 there was discovered an old well, lined with stone and filled with 

 estuary-mud, at a spot which previously had been, and now is, per- 

 manently submerged. In this case a movement of subsidence seems 

 to have taken place within a very recent period. 



It would then seem, that, taking the central Hue of the valley of 

 the Medina, there have been depressions on either side, east and 

 west (Newton River and Ryde). Beyond the Yarmouth valley the 

 late Prof. Edward Forbes noticed some evidences of recent elevation. 



On the extreme south of the Isle of Wis-ht there is evidence of like 

 unequal movements, which seems unexceptionable. There are three 

 headlands here lying east of one another ; of these, St. Catherine's 

 Down, 850 feet, is on the west, distant about three miles from Week 

 Down ; and at about one and a half further east, Shanklin Down or 



