(FIGURE 16. SECTION OF FLUVIO-MARINE STRATA, CONTAINING FLINT
IMPLEMENTS AND BONES OF EXTINCT MAMMALIA, AT MENCHECOURT,
ABBEVILLE.*
(* For detailed sections and maps of this district, see
Prestwich, "Philosophical Transactions" 1860 page 277.)
1. Brown clay with angular flints, and occasionally Chalk rubble,
unstratified, following the slope of the hill, probably of
subaerial origin, of very varying thickness, from 2 to 5 feet
and upwards.
2. Calcareous loam, buff-coloured, resembling loess, for the most
part unstratified, in some places with slight traces of
stratification, containing freshwater and land shells, with
bones of elephants, etc.; thickness about 15 feet.
3. Alternations of beds of gravel, marl, and sand, with
freshwater and land shells, and, in some of the lower sands,
a mixture of marine shells; also bones of elephant, rhinoceros,
etc., and flint implements; thickness about 12 feet.
a. Gravel underlying peat, age undetermined.
b. Layer of impervious clay, separating the gravel from the peat.)
To begin with the oldest, Number 3, it is made up of a succession of beds, chiefly of freshwater origin, but occasionally a mixture of marine and fluviatile shells is observed in it, proving that the sea sometimes gained upon the river, whether at high tides or when the fresh water was less in quantity during the dry season, and sometimes perhaps when the land was slightly depressed in level. All these accidents might occur again and again at the mouth of any river, and give rise to alternations of fluviatile and marine strata, such as are seen at Menchecourt.
In the lowest beds of gravel and sand in contact with the Chalk, flint hatchets, some perfect, others much rolled, have been found; and in a sandy bed in this position some workmen, whom I employed to sink a pit, found four flint knives. Above this sand and gravel occur beds of white and siliceous sand, containing shells of the genera Planorbis, Limnea, Paludina, Valvata, Cyclas, Cyrena, Helix, and others, all now natives of the same part of France, except Cyrena fluminalis (Figure 17), which no longer lives in Europe, but inhabits the Nile, and many parts of Asia, including Cashmere, where it abounds. No species of Cyrena is now met with in a living state in Europe. Mr. Prestwich first observed it fossil at Menchecourt, and it has since been found in two or three contiguous sand-pits, always in the fluvio-marine bed. [Note 16]
(FIGURE 17. Cyrena fluminalis, O.F. Muller, sp.*
(* For synonyms, see S. Woodward "Tibet Shells" "Proceedings
of the Zoological Society" July 8, 1856.)
a. Interior of left valve, from Gray's Thurrock, Essex.
b. Hinge of the same magnified.
c. Interior of right valve of a small specimen, from Shacklewell,
London.
d. Outer surface of right valve, from Erith, Kent.)
TABLE 8/1. DATES OF SPECIFIC NAMES.
COLUMN 1: SPECIES.
COLUMN 2: DATE.
LIVING:
Tellina fluminalis, O.F. Muller: 1774.
Venus fluminalis Euphratis, Chemnitz: 1782.
Cyclas Euphratica, Lam.: 1806.
Cyrena cor, Lam. (Nile): 1818.
Cyrena consobrina, Caillaud (Nile): 1823.
Cyrena Cashmiriensis, Desh.:
Corbicuia fluminalis, Muhlfeldt.: 1811.
FOSSIL:
Cyrena trigonula, S. Woodward: 1834.
Cyrena Gemmellarii, Philippi: 1836.
Cyrena Duchastelii, Nyst: 1838.