to a height of about 65 metres (but does not exist on the plateau), above which the upper gravels crop up to the surface. On the other hand, on descending towards the river the "terre à briques" increases in depth till it attains an average thickness of 1 metre. Since its original deposition it has, however, been more or less affected by ordinary denuding agencies, so that the washed-down materials have accumulated in certain hollows to a depth of 2 or 3 metres. Thus, at the Tellier brick-works the depth of the "terre à briques" is 2.50 metres, and at Renancourt, in the small valley of the Selle, it amounts to 3 metres. In the upper layers of these accumulations, Neolithic and even Roman and Mediaeval remains are not unfrequently met with.
Underneath the "terre à briques" lies a yellowish sandy clay called Ergeron, which is supposed to be a kind of loess, and contains flint implements of Palæolithic types. M. Comment has directed attention to the fact that at the junction between these two deposits, which probably at one time formed a habitable land-surface, he has found flint implements which may be paralleled with Magdalénien types. His discoveries are embodied in an illustrated paper, entitled "L'Industrie de la base de la terre à briques à Saint Acheul, Montières, Belloy-sur-Somme" (ibid., 1907, p. 239). A few of the flint objects described and figured by the author are represented on Plate IV., which will give some idea of their character, and the industrial stage to which they belong. They were found partly at the base of the "terre à briques," and partly embedded in the Ergeron at Saint Acheul (Nos. 10 to 21), Montières (8 and 9), and Belloy-sur-Somme (1 to 7). As will be seen from the illustrations, they represent most of the ordinary varieties of flint implements found in the upper deposits of the Palæolithic period, such as scrapers, flakes, burins, nuclei, etc.
The "terre à briques" is sometimes confounded with another reddish clay, described as "limon rouge sableux (limon fendillé)," which lies below the upper gravels, and is also used for making bricks and for foundry purposes. Especially is this the case when the former is absent, as sometimes happens in some of the pits. The "limon fendillé" lies over a whitish calcareous mud, called "terre à pipe." The stratigraphy of these different
