Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/732

530 on the line of strike of the general surface of the country, will illustrate its tabular character and the way in which the rivers intersect it. Theextension inland of the tableland is best seen on the east of the Avon, where it can be followed from the coast northwards for upwards of twenty miles to a gravel-capped escarpment, 420 feet above the sea, and 200 feet above the ground immediately to the northward, extending from Downton Common to Bramshaw. It is easy to see that the high plains, such as Picked Plain, Bratley Plain, and Ocknell Plain, although separated by deep valleys or " bottoms," form parts of one continuous tableland, and nowhere is this more evident than near the highest part between Downton, Fordingbridge, and Bramshaw. The eye there ranges over an extensive plateau curiously intersected by valleys 100 to 150 feet deep, by which the tabular appearance of the surface is, however, but little affected.

Section No. 3 commences at the coast near High Cliff, two miles east of the mouth of the Avon, where the cliff is 96 feet high, and is capped with 18 feet of gravel, and extends by two lines branching at Bratley Plain, to the northern escarpment near Bramshaw Telegraph, and at Blackbush Plain, respectively 419 feet and 397 feet above the sea. From the coast to the escarpment the ground has a uniform inclination of about 20 feet per mile, or one-fifth of a degree with the horizon. The surface is generally covered with gravel, which appears to thicken as the ground drops towards the valleys; the sides of the valleys are free from gravel, and the bottoms contain a gravel much mixed with locally derived clay and marl, and distinct from that covering the plains.

The regularity of the surface of the plains, where they are not cut up by streams, is very remarkable, more so on the ground than would perhaps appear from some of the sections, in which the vertical heights being necessarily greatly exaggerated, every irregularity is magnified to about thirteen times its natural scale.

To the westward of the Avon, the triangular tableland between Christchurch, Wimborne, and Poole is cut off on the north by the Stour valley. It varies in height from 100 feet near the coast to 190 feet towards Wimborne, and sections of the gravel covering it are seen along the coast, in the railway-cutting between Christchurch and Bournemouth, in the cutting south of Wimborne, and in numerous gravel-pits. On the north of the Stour at Wimborne, Canon Hill and Cole Hill are capped with gravels at a level corresponding to those of the plains to the south ; and still more inland, Chalbury Hill and Pistil Hill are covered with flint-gravel at greater elevations. The latter, a detached flat-topped hill, 320 feet above the sea, corresponds exactly in level with the plain on the opposite side of the Avon, and appears to be the remnant of a sloping tableland, of which the mass has undergone destruction by the action of the Stour, Blackwater, and Avon. Generally the country near the confluence of these rivers is at a much lower level than the high plains, ranging from 30 to 80 feet above the sea, or about 30 feet