Page:Quarterly Journal of the Geological Society of London, Volume 24.djvu/229

Rh TYLOR AMIENS GRAVEL.

Ill

These joints are now in many cases fissures two or three inches wide, and extending to a considerable depth ; but they are filled up with a fine brown loess, which seems as if injected into them ; for I observed in one or two cases that a vein of two or three inches thick had entered a horizontal joint, and passed along that in a horizontal direction, thinning out to only half an inch. I give a sketch of this chalk-quarry. This system of joints would very much facilitate the

Fig. 2. — Section exposed in a Chanc-qitarrtj near Gidgencourt.

formation, or rather the separation, of the chalk into rectangular and imperfect spheroids, such as are seen in the quarries behind St. Acheul and Longuean, where some decomposing agency has acted upon the chalk itself with considerable efiect.

In the drawing (fig. 3) made of the condition of the surface of the

Fig. 3. — Section along the St. Acheul and Longueau Road.

chalk (and to a depth of 20 feet) along the Saint-Acheul and Longueau road, running east and west, I found the sandpipes in the chalk very close together, and filled with brown loess and gravel. There are some large pipes in the eastern escarpment in M. Dailli's garden, close to the road ; but they decrease towards Cagny on the escarpment of chalk trending southwards there exposed, and also in the escarp- ment of chalk trending northwards. (See fig. 4.) I did not observe any

Fig. 4. — Section in M. Dailli's Garden showing

Chalk.

decomposed chalk in the railway- cutting or quarry between Longueau and La Neuville, nor at the ballast-pit in the chalk near La Neuville at the railway workshops, Amiens. The surface of the chalk, how- ever, is irregular, and covered with gravel, but without deep pipes.