A FRAGMENT OF THE GEOGRAPHY OF ENGLAND.

between 200 and 300 feet than in any other hundred feet interval of height until 600 feet is reached.

The contour-line of 50 feet, which forms the upper limit of the land below 50 feet in elevation, runs nearly from west to east across the southern part of Sheet 317 (Sheet 332 having no land at so high a level); but at the place where the Arun crosses the South Downs, the contour line runs northward, bounding the low land on each side of the river. The land below 50 feet is thus divided into the coastal plain, entirely south of lat. 50° 51′ and the river plain, which has a less regular form and much smaller area. The surface of the river plain is entirely covered with alluvium deposited by the stream in its meanderings. The coastal plain is mainly composed of Tertiary strata like those of the London basin, consisting of various sands and clays, although Chalk occurs in the east; but the whole is covered for the most part with drift composed of later gravels and brick-earth. Above the level of 50 feet these formations thin away rapidly, until about the elevation of 150 feet the solid Chalk of the South Downs appears at the surface. The Downs are composed entirely of Chalk, but the valleys which penetrate them from the south are carpeted with valley gravels. From the coastal plain the land rises comparatively gently (with a mean gradient above 300 feet of about 1 in 17) to the nearly flat summit; but towards the north the slope is much more abrupt (averaging, down to 300 feet, 1 in 3), plunging down to the plain of the Rother. This steep slope stops at an elevation of about 300 feet (near the transverse valley of the Arun not until a lower level), and here the Chalk ends, and the Rother valley is composed of a narrow terrace of the Upper Greensand, which at

FIG. 1.-SECTION ACROSS DISTRICT FROM NORTH TO SOUTH-THE BLACK

PORTION SHOWS TRUE SLOPES.

12.

13

14 Miles.

200 feet stops abruptly and gives place to wide parallel belts of Gault clay and various strata of the Lower Greensand, each successive belt emerging from under the foregoing. The surface is broken and irregular in contrast to the smoothness of the coastal plain and the rounded forms of the Downs, and after sinking to the level of 50 feet or under in the river bed, it rises again to the north to heights of over 400 feet, the harder Weald Clay with included Horsham stone occupying the north

FIG. 2.-SECTION ALONG RIDGE OF DOWNS ACROSS COCKING PASS.

eastern corner of the sheet. The sketch-map, Fig. 7, shows the main geological divisions. Fig. 1 shows the profile of the country from north to south both on a true scale and with the vertical scale exaggerated ten times. Figs. 2 and 3 show sections along the crest of the Downs across the valleys. Fig. 2 is a typical geological section along the same line as Fig. 1, showing how the successive beds crop out, and how the abrupt escarpment of the Chalk Downs facing the north is formed by the weathering away of the steep edge of the gently sloping stratum, the smooth and only slightly undulated outline of the slope contrasting with the deep valleys and long spurs which diversify the gentler declivity to the south.

The areas of the different geological formations, and the percentage they cover of the whole area of the land included in the sheets, are given below:

This table shows the preponderance of soil formed from drift and

Tertiary sands or clays like those of the London basin, and the insig nificant area of the Upper Greensand which, as will be shown presently, plays a very remarkable part in determining the distribution of the population north of the Chalk escarpment.

The Coastal Plain.-The declivity of the Downs on the southern side, although broken by valleys and spurs, becomes increasingly gradual as the Chalk dips below the overlying Tertiary formations,

FIG. 4.-GEOLOGICAL SECTION FROM NORTH TO SOUTH.
(SHOWING STRATA OUT OF WHICH THE SCENERY IS CARVED).

i.e. from 300 feet down to 50 feet. Below this level the slope is very slight indeed, the actual coast-line being formed for the most part by beds of clay, mounds of shingle, or drifted sand from 10 to 25 feet high. Inland, however, there are several considerable depressions. The gravel ridge at Selsey Bill, which forms the site of Selsey, is cut off from the mainland by a narrow marshy depression in part below sea-level, through which a little channel practically unites the sea at Pagham with the sea at Bracklesham Bay. Formerly this was a broad tidal marsh difficult to cross, emphasizing the isolation of the peninsula of Selsey. The bed of the disused Chichester and Arundel canal runs west and east from the tidal Chichester channel to the Arun river at an elevation of about 20 feet, somewhat higher land occurring to the south. The clays of the Tertiary formations and the overlying drift form excellent soil and are highly cultivated, while the lowlying marsh lands yield pasture. Throughout the whole coastal plain the underlying Chalk has been reached in borings for wells, in some places more than 300 feet below the surface. East of the Arun the Chalk is covered with drift only, and comes to the surface at several places. The Chalk foundations of the coastal plain have been formed by the erosion

of somewhat disturbed strata, and the drift laid down upon them by the action of sea-ice coming from the south.*

The coast-line formed by a gravel beach, above which a low clay cliff rises at some places, is undergoing great erosion. Off Selsey Bill a line of banks covered by less than 25 feet of water, traces out an earlier coast-line running parallel to the present shore and about 5 miles distant from it. Along the coast to the eastward the depth of 25 feet is reached everywhere within 1 mile of the low-water line. Below the shingle slope a broad beach of fine sand is laid bare at low water, the tide retiring for a mile or more at some points.

Historical evidence of the submergence of the old cathedral of Selsey amply confirms the deductions as to erosion which may be drawn from the map, and the rate at which the coast is now being eaten back is estimated at from 6 to 8 feet per aunum opposite Bracklesham Farm, and from 10 to 13 feet opposite Cockham Manor Farm.† At Pagham the old tidal harbour of 750 acres in extent was reclaimed in 1875-77, the sea being kept out by the great accumulation of shingle, and the land-water allowed to escape by a sluice.

The tides along the coast rise 16 feet at springs and 12 feet at neaps. An exceptionally high tide, especially if a strong south-westerly wind is also blowing, is apt to wash away the shingle beach and leave the land behind exposed to inundation. Between the embanked promenade at Bognor and the sandhills at the mouth of the Arun there are several places where the land is below high-tide level, and artificial banks have been built to keep the sea from the fields. At Felpham and Middleton much damage has been done by storms, the old churchyard of the latter parish having been washed away. The parish of Climping, at the mouth of the Arun, west of the river, includes about 80 acres, formerly part of the old parish of Cudlawe, or Cudlow, the greater part of which has been washed away, the site of the parish church being now occupied by 2 fathoms of water.

Along almost the whole shore included in the sheet, groynes of timber, or even of solid masonry and cement, have been erected at close intervals, running down the beach at right angles to high-water mark. Their object is to prevent the shingle and sand from being washed along the shore from west to east, and to cause accumulations against the weather side of the obstructions and so to pile up a defensive wall. The number of old groynes to be seen almost buried in the sand, shows that this method of combating the loss of land by erosion is a sound one (see photograph, Fig. 5).

The streams of the coastal plain are small and indefinite. River

* Memoir on Sheet 332 of the Geological Survey,' by Clement Reid.

+ Report on Coast Erosion. British Association Reports,' 1895, p. 374.

Kelly's 'Directory of Sussex.' 1899.