Somme, as at Saint Roch, others were 30 or 40 metres above the level of the river, and on both sides of the valley. G. de Mortillet informs us that he collected Chelléen types at an altitude of 50 or 60 metres (Le Préhistorique, p. 563).
Sir Charles Lyell gives a section across the valley showing the relation of the different deposits to each other.
Since the publication of the Antiquity of Man, further discoveries both at Abbeville and Amiens, especially those of M. Dault du Mesnil, have confirmed the presence of all the three elephants, as well as the Rhinoceros merckii, in the lowest strata, both in the high and low level gravels (Rev. de l'Ecole d'Anthrop., 1896, p. 286).
M. Commont, who has been for several years assiduously working out the complicated problems of the Somme Valley, especially at Saint Acheul, published an important paper on "L'Industrie des Graviers Supérieurs à Saint Acheul" (ibid., 1907, p. 15). On Plate III. are figured a few specimens of the flint implements from these gravels, Nos. 1 and 2 representing pre-Moustérien types, the so-called "limandes" and "ficrons" of the workmen. Nos. 3, 4, 7 represent the "Levallois flake," so named from its abundance among the flint industry found on the station of Levallois-Perret, near Paris, and regarded as the most characteristic implement of the Moustérien epoch. It is this special form which has given the coup de grace to the ovate and later Acheuléen implements, which, being chipped on both sides, ultimately became so thin that they were apt to break on usage. On the other hand, the Levallois flake was carefully chipped, but only on one side. The modus operandi in its manufacture is interesting. The operator, holding the raw flint nodule in his left hand, carefully chipped one surface, and then with a well-directed blow separated the entire worked surface from the rest of the nodule. The tools thus produced had sharp edges, and, being thicker in the middle and towards the bulb of percussion, they were more effective and less liable to be broken than the later Acheuléen specimens.
The upper part of the Quaternary deposit in the district of Saint Acheul forms a bed of reddish mud ("limon supérieurs ou terre à briques") which covers the slopes of the valley up
