TYLOR AMIKNS GllAVEL. 107 



C H is near the Imperial lload, and is parallel to that road, to 

 the railwaj% and to the lliver Somrae. 



Section G H.—The length of G H is 1400 feet. See Tlate IV. fig. 5. 

 The highest point is 157 feet above the sea, 79 feet above the lliver 

 Arve, 3 feet over the highest part of the Imperial road, (31 feet 

 above the rails, and 84 feet above the lliver Somme at Neuville. 

 The gradient, commencing at point H, 129 feet above the sea. Hue 

 de Cagny, rises to the east 1 in 30, then 1 in 33, 1 in 35, 1 in 61, 

 and 1 in 100, reaching the well-known section of St.-Acheul Pit, 

 with Koman graves, fossiliferous sand, and wavy marls, at a height 

 of 152 1 feet above the sea. A portion of this is shown in Plate IV. 

 fig. 12. 



The loess in this section is four feet at the highest and most east- 

 erly point, G, gradually thinning to the west, and ceasing when it 

 reaches H. 



The gravel is sixteen feet thick at its most easterly point, G, thin- 

 ning out as it passes to the west a little before the loess disappears. 



The surface of the chalk is 133 feet above the sea at G, and 128 

 feet at H. The surface falls 1 in 280 to the west. 



Section E F. — The surface gradient commences at P, at a height 

 of 156 feet above the sea, and it passes the Cemetery Road on the 

 level, and rises at a gradient to the east of only 1 in 700, then falls • 

 to the east at 1 in 165 and 1 in 701, reaching the point E at a 

 height of 154 feet above the sea (Plate IV. fig. 4). 



The loess is 4 feet at P, thickening to 5 feet at the summit-level 

 of the whole section C H, and then thinning out to 4 feet at E. The 

 regularity of the loess is a very important fact. 



The gravel is 17 feet thick at P, and 15 feet at E. The surface of 

 the chalk is 133 feet above the sea at both E and P, showing a 

 perfectly horizontal line, while there is only a variation in the level 

 of the surface-loess of 3 feet in this section, which is 1586 feet 

 long. 



Section (72) (Plate IV. fig. 3). — Section C D commences at D with 

 an elevation of 153| feet above the sea ; and the gradient falls east 

 at 1 in 157, then rises to the east 1 in 80, then falls to the east 1 in 

 40 and 1 in 300. Here the tramway (Plate IV. fig. 1) crosses the 

 Imperial Road, and some very extensive gravel-pits are now being 

 worked for ballast. 



The gradient continues falling east 1 in 88, 1 in 180, 1 in 160, 

 1 in 41, 1 in 33, and rising 1 in 200 to the east, where it reaches 

 the escarpment at a height of 142^ feet above the sea. The loess is 

 here 5 feet thick, and the gravel 2 feet, according to M. Guillom's 

 survey ; but I found only two or three feet where I observed it. The 

 loess is 5 feet thick near the tramway, and 4 feet at the point D. 

 The gravel is 13 feet thick at D, and 10 feet thick at the tramway, 

 thinning out as it approaches the escarpment on the east, as it did 

 on the west. The surface of chalk is horizontal throughout this sec- 

 tion also up to the escarpment. 



At the escarpment the chalk falls to the east 52| feet in a distance 

 of 106, or at an angle of 45° and gradient of 1 in 2 nearly. The line 



