86 SCIENCE PROGRESS 



typical Chellean on the second terrace and Chelleen evolue on 

 the first. 1 



Acheulean, — With the advent of this period the distinction 

 between subaerial and fluviatile deposits becomes important, 

 since according to M. Commont the series of beds {Unions moyens 

 or loss ancien) in which these implements occur in the Somme 

 valley belong entirely to the former category 2 ; and thus 

 we are able to account, without postulating a series of earth- 

 movements, for the fact that the industry is not confined to 

 any one terrace but ranges from the lowest terrace up to the 

 plateau above, 55 metres higher than the river-bed. M. Com- 

 mont is of opinion 3 that at the close of the Chellean period, 

 after the formation of the first terrace, a depression of the 

 land occurred which gave rise to the raised beaches of Brighton, 

 Sangatte, etc., and caused the deposition of marine shells on 

 the second terrace at Menchecourt ; and the loss ancien, with 

 Acheulean implements, is assigned to the period immediately 

 following this. The arguments, however, on which this opinion 

 is based are not very convincing, and appear to rely too much 

 on the supposed contemporaneity of beds containing Corbicula 

 fluminalis at Menchecourt and under some ancient dunes ; but 

 as that mollusc is found in pre-Chellean gravel at Swans- 

 combe, 4 and again in brick-earth at Crayford (about 40 ft. O.D.) 

 associated with Mousterian flakes, 5 it cannot be regarded as a 

 zone fossil of Chellean times. 



Although Acheulean implements are classed by M. Com- 

 mont as typical products of the first terrace, 6 they are absent 

 from this level at several stations, 7 and appear to be more 

 particularly associated with the second terrace, but not with 

 its fluviatile deposits. 



In Belgium the general succession of strata and their rela- 

 tion to Acheulean man accords closely with that of France, 

 but M. Rutot regards the beds covering these implements as 

 the relics of gigantic floods, and not of subaerial origin. 



In England the evidence is still somewhat imperfect ; but 



1 V. Commont, Les Homines Conlemporains du Renne, pp. 39-42. 



2 Ibid. pp. 28 and 38. 



3 Ann. Soc. Ge'ol. du Nord, vol. xxxix. (1910), p. 207. 

 * Archaologia, vol. lxv. (1914), p. 192. 



5 Proc. Geo/. Assoc, vol. xxv. (1914), p- 64. 



6 Ann. Soc. Ge'ol. du Nord, vol. xxxix. (1910), p. 292. 



7 Ibid. p. 208 ; Les Hommes Contemporains, etc., p. 42. 



