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

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108
PROCEEDINGS OF THE GEOLOGICAL SOCIETY.

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