Page:Quarterly Journal of the Geological Society of London, Volume 24.djvu/226

108 108 PROCEEDINGS OF THE GEOLOGICAL SOCIETY.

of slope of this escarpment is remarkably straight in many places, and quite free from gravel or loess. Then there follows a flat ter- race of loess, 60 feet wide, then a slope towards the river, of 1 in 30, and then 1 in 4, until we reach the marsh at a height of 76^ feet above the sea.

III. Descriptions of the Transverse Sections.

Section I Z" (Plate lY. fig. 6). — This section commences at the Rue de Cagny, point I, at a height of 200 feet above the sea, and falls to the river and the north at a gradient of 1 in 32, 1 in 28, 1 in 22, 1 in 18, 1 in 54. It then rises to the north at 1 in 162, and crosses the tramway ballast-pit at a level of 153^ feet above the sea, and the Imperial E-oad at a height of 153 feet above the sea ; it then rises to the north at a gradient of 1 in 20, reaching 156 feet above the sea, then falls towards the river at 1 in 42, 1 in 100, rises 1 in 87, falls 1 in 67, 1 in 65, 1 in 50, until it reaches the railway- cutting, at a height of 138 feet above the sea. The cutting happens to be in the escarpment of the ancient chalk vaUey, in which the valley-gravel has been deposited; and the surface of the gravel follows the contour of the ground, and falls at a gradient of . 1 in 8, and then 1 in 7, declining 47 feet in a distance of 360 feet. The surface then faUs more gently to the river at 1 in 36, 1 in 34, until it reaches the Somme.

At the Point I in the Eue.de Cagny the loess is 3 feet thick, and near the Imperial Eoad it is 8 feet thick : at one point it gradually thins out towards the river and railway, and at the railway- cutting the loess is only 2 feet thick. I do not know the thickness on the north side of the railway ; but as the gravel thins out rapidly, the loess is no doubt from 10 to 12 feet thick in some points. The gravel at the point I is 5 feet thick ; it increases to 10 feet thick as it approaches the Imperial Eoad, and after passing that at a height of 148 feet above the sea it gradually thins away until it is only 3 feet thick at the south side of the railway- cutting, and soon merges into the loess on the steep incline on the north side of the railway.

The surface of the chalk at the Eue de Cagny near the point I is 195 feet above the sea ; it falls to 136 feet above the sea where it passes under the Imperial Eoad, and then becomes nearly horizontal, only falling 3 feet until it reaches the railway-cutting.

Fig. 1. — Section at La NeuviUe, showing the Loess resting immediately on the Chalk.

The slope then becomes rapid again, and it probably falls at a