EYIDEXCES OF THE GEOLOGICAL AGE, ETC. 



407 



tlie north-west of the town. The deposit there is Tery distinct in its character, 

 and occnrs as a patch on the side of a chalk hill, which commands it to the 

 northward, while it slopes down under the peat-beds of the vaUey of the 

 Somme to the southward. The following is the section in descending order, as 

 given by jMr. Prestwich. 



Average 

 thickness. 



1. A mass of brown sandy clay, with angular fragments of 

 flints and chalk-rubble. 'No organic remains. Base 



very irregular and indented into bed No. 2 2 to 12 feet, 



2. A light-coloured sandy clay ("sable gras" of the work- 

 men) analogous to the loess, containing land-shells, Piq)a, 

 Helix, Clausilia^ of recent species. Elint-axes and mam- 

 malian remaias are said to occur occasionally in this bed 8 to 25 feet. 



3. White sand (" sable aigre"), Avith one to two feet of 

 sub-angular flint -gravel at base. This bed abounds in 

 land- and fresh-water-shells of recent species of the 

 genera Helix, Succinea, Cyclas, Pisiditm, Valvata, Bithy- 

 nia, and Planorhis, together with the marine Buccinum 

 undatum, Cardiim edide, Tellina soUdtda, and Hurpura 

 lapilhis. The author has also found the Cyrena conso- 

 hrina and Litorina rudis. With them are associated 

 numerous mammalian remains, and it is said flint imple- 

 ments 2 to 6 feet. 



4. Light-coloured sandy marl, in places very hard, with 



Helix, Zofiites, Succinea, and Bupa. Not traversed 3 feet. 



M. Buteux enumerates from this pit the remams of 'Elephas primigenius^ 

 RJiinocews tichorJiinus, Cermis Somonensis, (?), C. tarandiis, C. pyiscus, Ursus 

 spelmis, Hy(Bna spel^sa, Bos priraigenius, Bquus adamaticus, and Felis. 



Of this section, however, Mr. Prest^'ich remarks that the essential work has 

 yet to be done, namely, the determination of the manner in which these fossils 

 are distributed, which occur in strata Nos. 2 and 3. "A few marine shells," 

 that geologist tells us, " occur mixed indiscrimmately with the freshwater 

 species, chiefly amongst the flints at the base of No. 3. They are very friable, 

 and somewhat scarce. It is on the top of this bed of flints that the greater 

 number of bones are found, and also, it is said, the greater number of flint 

 implements."" Mr. Prest\A-ich, however, only saw some long flint flakes (con- 

 sidered by M. de Perthes as flint knives) from the peat-beds and barrows. 

 There are specimens, however, of the larger implements, or " haches," from 

 Menchecourt, in M. de Perthes' collection ; one from a recorded depth of five 

 metres, and another from a recorded depth of seven metres. This would take 

 them out of No. 1 stratum, but leaves it uncertain whether they came from 

 No. 2 or No. 3. Prom this general appearance, Mr. PrestAvich is disposed to 

 place them in bed No. 2, but M. de Perthes believes them to be from No. 3 — 

 if so, Mr. Prestwich thinks they must have come from some subordinate clay- 

 seams occasionally intercalated in the white sand. 



With regard to the geological age of these beds, Mr. Prestwich considers 

 them as belonging to the period usually designated as Post-pliocene, and 

 notices their agreement with many beds of that age in England. The Menche- 

 court deposit thus resembles that of Pisherton, near Salisbury ; the gravel of 

 St. Acheul is like some on the Sussex coast ; that of Moulin Quignon resem- 

 bles the gravel so well exposed in the great railway ballast-excavation at East 

 Croydon, and the gravel at Wandsworth-common, and many other places round 

 London. 



