KVIDENCES OF TIIK GEOLOGICAL A(iE, ETC. 
407 
tliC uorth-wcsl of t lio town. Tlic deposit, there is very distinct in its eiuiracler, 
and oceurs as a patcli on the side of a clialk hill, whicii commands it to the 
nortliward, while it slopes down under the jicat-beds of the valley of the 
Somme to the southward. The following is the section in descending order, as 
given by Mr. Prestwick. 
Average 
thickness. 
1. A mass of brown sandy clay, witli angular fragments of 
flints and chalk-rubble. No organic remains. Base 
very irregidar 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, Pi(pa, 
Helix, ClamiUa, of recent species. Flint-axes and nuim- 
malian remains are said to occm- occasionally in this bed 8 to 25 feet. 
3. White saud ("sable aigre"), with one to two feet of 
sub-angular Hint -gravel at base. This bed abounds in 
land- and frcsli-water-shells of recent species of the 
genera Helix, Siirciiwa, Ci/clas, Pisiflium, Valcata, Bithy- 
nia, and Planorbis, together with the marine Buccinum 
undatum, Cardium edule, Tellina solidula, and Purpura 
lapillus. The author has also found the Cyrena conso- 
brina 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, Zonites, Succinea, and Pupa. Not traversed 3 feet. 
M. Buteux enumerates from this pit the remams of Elephas primigeniusy 
RJiinoceros ticliorhinm, Cervus Somonensis, (?), C. taraiidus, C. prisciis, Ursus 
speleeus, Hi/mia spelcea. Bos primitjenitcs, Eqtms adumalicus, and Felis. 
Of this section, however, Mr. Prestwich remarks that the essential work has 
yet to be done, namely, the determination of the manner in wbich these fossils 
are distributed, which occur in strata Nos. 2 and 3. " A few marine shells," 
that geologist tells us, " occur mixed indiscriminately 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. Prestwich, 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 " baches," from 
Menchccourt, 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. Prestw'ich is disposed to 
place them in bed No. 2, but M. de Perthes beheves them to be from No. 3 — 
if so, Mr. Prestwich thinks they must have come from some subordinate clay- 
scams 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-jiliocene, and 
notices their agreement with many beds of that age in England. The Menchc- 
court deposit thus resembles that of Pisherton, near Salisbury ; the gravel of 
St. Acheul is like some on the Sussex coast ; that of Moulin Quiguon 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. 
