Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/733

1870.] above the rivers. Somerley Heath, and Alderholt Heath, although 130 feet above the sea, are still 170 feet lower than the plains on the other side of the Avon, and immediately opposite them.

The bottom of the valley of the Avon is shown by a dotted line on section No. 3. Its fall is at the rate of from 8 feet per mile near Hale to 3 feet per mile near the sea; so that while the tableland near Christchurch is but 83 feet above the valley, at Hale the high plain of Hatchet Green is 300 feet above it.

Bordering on the valley between Fordingbridge and Ringwood, at levels approaching the tableland in height, there are terrace-like plains, which are well seen from the high ground on the opposite or western side of the valley.

On the east of section No. 3 the gravel-covered tableland stretches northward from Barton and Hordwell Cliffs till it is interrupted by the Avon-water valley. The tabular character is carried on by plains at corresponding levels near Wilverley; and beyond an area comparatively low, and drained by numerous tributaries of the Boldre river, is the high ground near Stoney Cross and Castle Malwood, which is continuous with Ocknell Plain, 270 feet above the sea, and gravel-covered. Section No. 4 illustrates the rise of the tableland from the coast to the Avon-water valley and to Wilverley, and shows how a prolongation of the same slope northwards would coincide with the high ground near Stoney Cross.

A section of the gravel covering the tableland is seen in the cliffs between Poole Harbour and the entrance of the Solent. Westward of Poole Harbour there is no gravel on the coast, though a patch occurs at a high level in the valley of the Frome near Rempston House; but between Poole and Bournemouth the cliffs are capped with gravel at from 100 to 120 feet above the sea. It is from this gravel that the flint implements found on each side of Bournemouth are derived. The section in the cliffs is nearly the same as that shown in section No. 2, the general level of the tableland near the coast at Bournemouth being about 120 feet above the sea. Except where it is intersected by the Bournemouth valley or by chines, the gravel-bed is continuous, and from 8 to 15 feet thick, to within about a mile from the mouth of the Avon; there the tableland ends, and a cliff not more than 10 or 20 feet high, is composed of what appear to be the gravel-beds of an old channel of the Avon or Stour, which reach as low as high-water mark. Between them and the present mouth of the river, Hengistbury Head rises to 120 feet, and is capped with the older gravel. About a mile eastward from the mouth of the Avon, the junction of the valley-gravels with the gravel of the plains is seen near Highcliff, and was noticed long ago by Sir Charles Lyell and by Mr. Godwin-Austen. From this point to Milford the gravel is again continuous, except where Chuton Bunny and Becton Bunny cut through it. In Barton and Hordwell cliffs the thickness is now as much as from 18 to 20 feet,