Geological Structure of the Valley of the Somme and of the
surrounding Country.
Position of Alluvium of different Ages.
Peat near Abbeville.
Its animal and vegetable Contents.
Works of Art in Peat.
Probable Antiquity of the Peat, and Changes of Level
since its Growth began.
Flint Implements of antique Type in older Alluvium.
Their various Forms and great Numbers.
GEOLOGICAL STRUCTURE OF THE SOMME VALLEY.
The valley of the Somme in Picardy, alluded to in the last chapter, is
situated geologically in a region of white Chalk with flints, the strata
of which are nearly horizontal. The Chalk hills which bound the valley
are almost everywhere between 200 and 300 feet in height. On ascending
to that elevation, we find ourselves on an extensive table-land, in
which there are slight elevations and depressions. The white Chalk
itself is scarcely ever exposed at the surface on this plateau, although
seen on the slopes of the hills, as at b and c (Figure 7). The general
surface of the upland region is covered continuously for miles in every
direction by loam or brick-earth (Number 4), about 5 feet thick, devoid
of fossils. To the wide extent of this loam the soil of Picardy chiefly
owes its great fertility. Here and there we also observe, on the Chalk,
outlying patches of Tertiary sand and clay (Number 5, Figure 7), with
Eocene fossils, the remnants of a formation once more extensive, and
which probably once spread in one continuous mass over the Chalk,
before the present system of valleys had begun to be shaped out. It is
necessary to allude to these relics of Tertiary strata, of which the
larger part is missing, because their denudation has contributed largely
to furnish the materials of gravels in which the flint implements and
bones of extinct mammalia are entombed. From this source have been
derived not only the regular-formed egg-shaped pebbles, so common in
the old fluviatile alluvium at all levels, but those huge masses of
hard sandstone, several feet in diameter, to which I shall allude in the
sequel. The upland loam also (Number 4) has often, in no slight degree,
been formed at the expense of the same Tertiary sands and clays, as is
attested by its becoming more or less sandy or argillaceous, according
to the nature of the nearest Eocene outlier in the neighbourhood.
The average width of the valley of the Somme between Amiens and
Abbeville is one mile. The height, therefore, of the hills, in relation
to the river-plain, could not be correctly represented in the annexed
diagram (Figure 7), as they would have to be reduced in altitude; or if
not, it would be necessary to make the space between c and b four times
as great. The dimensions also of the masses, of drift or alluvium, 2
and 3, have been exaggerated, in order to render them sufficiently
conspicuous; for, all important as we shall find them to be as
geological monuments of the Pleistocene period, they form a truly
insignificant feature in the general structure of the country, so much
so, that they might easily be overlooked in a cursory survey of the
district, and are usually unnoticed in geological maps not specially
devoted to the superficial formations.
[Illustration: Figure 7. Valley of the Somme]
(FIGURE 7. SECTION ACROSS THE VALLEY OF THE SOMME IN PICARDY.
1. Peat, 20 to 30 feet thick, resting on gravel, a.
2. Lower level gravel with elephants' bones and flint tools,
covered with fluviatile loam, 20 to 40 feet thick.
3. Higher level gravel with similar fossils, and with overlying
loam, in all 30 feet thick.
4. Upland loam without shells (Limon des plateaux), 5 or 6
feet thick.
5. Eocene strata, resting on the Chalk in patches.)
It will be seen by the description given of the section (Figure 7) that
Number 2 indicates the lower level gravels, and Number 3 the higher
ones, or those rising to elevations of 80 or 100 feet above the river.
Newer than these is the peat Number 1, which is from 10 to 30 feet in
thickness, and which is not only of later date than the alluvium, 2 and
3, but is also posterior to the denudation of those gravels, or to the
time when the valley was excavated through them. Underneath the peat is
a bed of gravel, a, from 3 to 14 feet thick, which rests on undisturbed
Chalk. This gravel was probably formed, in part at least, when the
valley was scooped out to its present depth, since which time no
geological change has taken place, except the growth of the peat, and
certain oscillations in the general level of the country, to which we
shall allude by and by. A thin layer of impervious clay separates the
gravel a from the peat Number 1, and seems to have been a necessary
preliminary to the growth of the peat.
PEAT OF THE VALLEY OF THE SOMME.
As hitherto, in our retrospective survey, we have been obliged, for
the sake of proceeding from the known to the less known, to reverse the
natural order of history, and to treat of the newer before the older
formations, I shall begin my account of the geological monuments of the
valley of the Somme by saying something of the most modern of all of
them, the peat. This substance occupies the lower parts of the valley
far above Amiens, and below Abbeville as far as the sea. It has already
been stated to be in some places 30 feet thick, and is even occasionally
more than 30 feet, corresponding in that respect to the Danish mosses
before described (Chapter 2). Like them, it belongs to the Recent
period; all the embedded mammalia, as well as the shells, being of the
same species as those now inhabiting Europe. The bones of quadrupeds are
very numerous, as I can bear witness, having seen them brought up from
a considerable depth near Abbeville, almost as often as the dredging
instrument was used. Besides remains of the beaver, I was shown, in the
collection of M. Boucher de Perthes, two perfect lower jaws with teeth
of the bear, Ursus arctos; and in the Paris Museum there is another
specimen, also from the Abbeville peat.
The list of mammalia already comprises a large proportion of those
proper to the Swiss lake-dwellings, and to the shell-mounds and peat of
Denmark; but unfortunately as yet no special study has been made of the
French fauna, like that by which the Danish and Swiss zoologists and
botanists have enabled us to compare the wild and tame animals and the
vegetation of the age of stone with that of the age of iron.
Notwithstanding the abundance of mammalian bones in the peat, and the
frequency of stone implements of the Celtic and Gallo-Roman periods, M.
Boucher de Perthes has only met with three or four fragments of human
skeletons.
At some depth in certain places in the valley near Abbeville, the trunks
of alders have been found standing erect as they grew, with their roots
fixed in an ancient soil, afterwards covered with peat. Stems of the
hazel, and nuts of the same, abound; trunks, also, of the oak and
walnut. The peat extends to the coast, and is there seen passing under
the sand-dunes and below the sea-level. At the mouth of the river
Canche, which joins the sea near the embouchure of the Somme, yew trees,
firs, oaks, and hazels have been dug out of peat, which is there worked
for fuel, and is about three feet thick.*
(* D'Archiac, "Histoire des Progres" volume 2 page 154.)
During great storms, large masses of compact peat, enclosing trunks of
flattened trees, have been thrown up on the coast at the mouth of the
Somme; seeming to indicate that there has been a subsidence of the land
and a consequent submergence of what was once a westward continuation of
the valley of the Somme into what is now a part of the English Channel.
Whether the vegetation of the lowest layers of peat differed as to the
geographical distribution of some of the trees from the middle, and this
from the uppermost peat, as in Denmark, has not yet been ascertained;
nor have careful observations been made with a view of calculating the
minimum of time which the accumulation of so dense a mass of vegetable
matter must have taken. A foot in thickness of highly compressed peat,
such as is sometimes reached in the bottom of the bogs, is obviously
the equivalent in time of a much greater thickness of peat of spongy
and loose texture, found near the surface. The workmen who cut peat, or
dredge it up from the bottom of swamps and ponds, declare that in the
course of their lives none of the hollows which they have found, or
caused by extracting peat, have ever been refilled, even to a small
extent. They deny, therefore, that the peat grows. This, as M. Boucher
de Perthes observes, is a mistake; but it implies that the increase in
one generation is not very appreciable by the unscientific.
The antiquary finds near the surface Gallo-Roman remains, and still
deeper Celtic weapons of the stone period. [14] But the depth at which
Roman works of art occur varies in different places, and is no sure test
of age; because in some parts of the swamps, especially near the river,
the peat is often so fluid that heavy substances may sink through it,
carried down by their own gravity. In one case, however, M. Boucher de
Perthes observed several large flat dishes of Roman pottery, lying in a
horizontal position in the peat, the shape of which must have prevented
them from sinking or penetrating through the underlying peat. Allowing
about fourteen centuries for the growth of the superincumbent vegetable
matter, he calculated that the thickness gained in a hundred years would
be no more than three centimetres.*
(* "Antiquites Celtiques" volume 2 page 134.)
This rate of increase would demand so many thousands of years for the
formation of the entire thickness of 30 feet that we must hesitate
before adopting it as a chronometric scale. Yet, by multiplying
observations of this kind, and bringing one to bear upon and check
another, we may eventually succeed in obtaining data for estimating the
age of the peaty deposit. [15]
The rate of increase in Denmark may not be applicable to France; because
differences in the humidity of the climate, or in the intensity and
duration of summer's heat and winter's cold, as well as diversity in the
species of plants which most abound, would cause the peat to grow more
or less rapidly, not only when we compare two distinct countries in
Europe, but the same country at two successive periods.
I have already alluded to some facts which favour the idea that there
has been a change of level on the coast since the peat began to grow.
This conclusion seems confirmed by the mere thickness of peat at
Abbeville, and the occurrence of alder and hazel-wood near the bottom of
it. If 30 feet of peat were now removed, the sea would flow up and fill
the valley for miles above Abbeville. Yet this vegetable matter is all
of supra-marine origin, for where shells occur in it they are all of
terrestrial or fluviatile kinds, so that it must have grown above the
sea-level when the land was more elevated than now. We have already
seen what changes in the relative level of sea and land have occurred
in Scotland subsequently to the time of the Romans, and are therefore
prepared to meet with proofs of similar movements in Picardy. In that
country they have probably not been confined simply to subsidence, but
have comprised oscillations in the level of the land, by which marine
shells of the Pleistocene period have been raised some 10 feet or more
above the level of the sea.
Small as is the progress hitherto made in interpreting the pages of the
peaty record, their importance in the valley of the Somme is enhanced by
the reflection that, whatever be the number of centuries to which they
relate, they belong to times posterior to the ancient implement-bearing
beds, which we are next to consider, and are even separated from them,
as we shall see, by an interval far greater than that which divides the
earliest strata of the peat from the latest.
FLINT IMPLEMENTS OF THE PLEISTOCENE PERIOD IN THE VALLEY OF THE SOMME.
The alluvium of the valley of the Somme exhibits nothing extraordinary
or exceptional in its position or external appearance, nor in the
arrangement or composition of its materials, nor in its organic remains;
in all these characters it might be matched by the drift of a hundred
other valleys in France or England. Its claim to our peculiar attention
is derived from the wonderful number of flint tools, of a very antique
type, which, as stated in the last chapter, occur in undisturbed strata,
associated with the bones of extinct quadrupeds.
As much doubt has been cast on the question, whether the so-called
flint hatchets have really been shaped by the hands of Man, it will be
desirable to begin by satisfying the reader's mind on that point, before
inviting him to study the details of sections of successive beds of mud,
sand, and gravel, which vary considerably even in contiguous localities.
Since the spring of 1859, I have paid three visits to the Valley of the
Somme, and examined all the principal localities of these flint tools.
In my excursions around Abbeville, I was accompanied by M. Boucher de
Perthes, and during one of my explorations in the Amiens district,
by Mr. Prestwitch. The first time I entered the pits at St. Acheul, I
obtained seventy flint instruments, all of them collected from the drift
in the course of the preceding five or six weeks. The two prevailing
forms of these tools are represented in the annexed Figures 8 and 9,
each of which are half the size of the originals; the first being the
spear-headed form, varying in length from six to eight inches; the
second, the oval form, which is not unlike some stone implements, used
to this day as hatchets and tomahawks by natives of Australia, but with
this difference, that the edge in the Australian weapons (as in the case
of those called celts in Europe) has been produced by friction, whereas
the cutting edge in the old tools of the valley of the Somme was always
gained by the simple fracture of the flint, and by the repetition of
many dexterous blows.
The oval-shaped Australian weapons, however, differ in being sharpened
at one end only. The other, though reduced by fracture to the same
general form, is left rough, in which state it is fixed into a cleft
stick, which serves as a handle. To this it is firmly bound by thin
straps of opossum's hide. One of these tools, now in my possession, was
given me by Mr. Farquharson of Haughton, who saw a native using it in
1854 on the Auburn river, in Burnet district, North Australia.
Out of more than a hundred flint implements which I obtained at St.
Acheul, not a few had their edges more or less fractured or worn, either
by use as instruments before they were buried in gravel, or by being
rolled in the river's bed.
Some of these tools were probably used as weapons, both of war and
of the chase, others to grub up roots, cut down trees, and scoop out
canoes. Some of them may have served, as Mr. Prestwich has suggested,
for cutting holes in the ice both for fishing and for obtaining
water, as will be explained in the eighth chapter when we consider
the arguments in favour of the higher level drift having belonged to a
period when the rivers were frozen over for several months every winter.
[Illustration: Figure 8. Flint Implement]
(FIGURE 8. FLINT IMPLEMENT FROM ST. ACHEUL, NEAR AMIENS,
OF THE SPEAR-HEAD SHAPE
(half the size of the original, which is 7 1/2 inches long).
a. Side view.
b. Same seen edgewise.
These spear-headed implements have been found in greater number,
proportionally to the oval ones, in the upper level gravel at St.
Acheul, than in any of the lower gravels in the valley of the Somme. In
these last the oval form predominates, especially at Abbeville.)
When the natural form of a Chalk-flint presented a suitable handle at
one end, as in the specimen, Figure 10, that part was left as found. The
portion, for example, between b and c has probably not been altered; the
protuberances which are fractured having been broken off by river action
before the flint was chipped artificially. The other extremity, a, has
been worked till it acquired a proper shape and cutting edge.
[Illustration: Figures 9 and 10. Flint Implements]
(FIGURES 9 AND 10. FLINT IMPLEMENTS FROM THE PLEISTOCENE DRIFT OF
ABBEVILLE AND AMIENS.
FIGURE 9. a. OVAL-SHAPED FLINT HATCHET FROM MAUTORT,
NEAR ABBEVILLE,
half size of original, which is 5 1/2 inches long, from
a bed of gravel underlying the fluvio-marine stratum. b. Same seen
edgewise. c. Shows a recent fracture of the edge of the same at the
point a, or near the top. This portion of the tool, c, is drawn of
the natural size, the black central part being the unaltered flint,
the white outer coating, the layer which has been formed by
discoloration or bleaching since the tool was first made. The
entire surface of Number 9 must have been black when first shaped,
and the bleaching to such a depth must have been the work of time,
whether produced by exposure to the sun and air before it was
embedded, or afterwards when it lay deep in the soil.
FIGURE 10. FLINT TOOL FROM ST. ACHEUL, seen edgewise;
original 6 1/2 inches long, and 3 inches wide.
b, c. Portion not artificially shaped.
a, b. Part chipped into shape, and having a cutting edge at a.)
Many of the hatchets are stained of an ochreous-yellow colour, when they
have been buried in yellow gravel, others have acquired white or brown
tints, according to the matrix in which they have been enclosed.
This accordance in the colouring of the flint tools with the character
of the bed from which they have come, indicates, says Mr. Prestwich, not
only a real derivation from such strata, but also a sojourn therein of
equal duration to that of the naturally broken flints forming part of
the same beds.*
(* "Philosophical Transactions" 1861 page 297.)
[Illustration: Figures 11, 12 and 13. Dendrites on Fling Hatchets]
(FIGURES 11, 12 AND 13. DENDRITES ON SURFACES OF FLINT HATCHETS IN
THE DRIFT OF ST. ACHEUL, NEAR AMIENS.
FIGURE 11. a. Natural size.
FIGURE 12. b. Natural size. c. Magnified.
FIGURE 13. d. Natural size.
e. Magnified.)
The surface of many of the tools is encrusted with a film of carbonate
of lime, while others are adorned by those ramifying crystallisations
called dendrites (see Figures 11, 12 and 13), usually consisting of the
mixed oxides of iron and manganese, forming extremely delicate blackish
brown sprigs, resembling the smaller kinds of sea weed. They are a
useful test of antiquity when suspicions are entertained of the workmen
having forged the hatchets which they offer for sale. The most general
test, however, of the genuineness of the implements obtained by purchase
is their superficial varnish-like or vitreous gloss, as contrasted with
the dull aspect of freshly fractured flints. I also remarked, during
each of my three visits to Amiens, that there were some extensive
gravel-pits, such as those of Montiers and St. Roch, agreeing in their
geological character with those of St. Acheul, and only a mile or
two distant, where the workmen, although familiar with the forms, and
knowing the marketable value of the articles above described, assured me
that they had never been able to find a single implement.
Respecting the authenticity of the tools as works of art, Professor
Ramsay, than whom no one could be a more competent judge, observes: "For
more than twenty years, like others of my craft, I have daily handled
stones, whether fashioned by nature or art; and the flint hatchets of
Amiens and Abbeville seem to me as clearly works of art as any Sheffield
whittle."*
(* "Athenaeum" July 16, 1859.)
Mr. Evans classifies the implements under three heads, two of which,
the spear heads and the oval or almond-shaped kinds, have already been
described. The third form (Figure 14) consists of flakes, apparently
intended for knives or some of the smaller ones for arrow heads.
[Illustration: Figure 14. Flint Knife or Flake]
(FIGURE 14. FLINT KNIFE OR FLAKE FROM BELOW THE SAND CONTAINING
CYRENA FLUMINALIS. MENCHECOURT, ABBEVILLE.
d. Transverse section along the line of fracture, b, c.
Size, two-thirds of the original.)
In regard to their origin, Mr. Evans observes that there is a uniformity
of shape, a correctness of outline, and a sharpness about the cutting
edges and points, which cannot be due to anything but design.*
(* "Archaeologia" volume 38.)
Of these knives and flakes, I obtained several specimens from a pit
which I caused to be dug at Abbeville, in sand in contact with the
Chalk, and below certain fluvio-marine beds, which will be alluded to in
the next chapter.
Between the spear-head and oval shapes, there are various intermediate
gradations, and there are also a vast variety of very rude implements,
many of which may have been rejected as failures, and others struck off
as chips in the course of manufacturing the more perfect ones. Some
of these chips can only be recognised by an experienced eye as bearing
marks of human workmanship.
It has often been asked, how, without the use of metallic hammers, so
many of these oval and spear-headed tools could have been wrought into
so uniform a shape. Mr. Evans, in order experimentally to illustrate the
process, constructed a stone hammer, by mounting a pebble in a wooden
handle, and with this tool struck off flakes from the edge on both sides
of a Chalk flint, till it acquired precisely the same shape as the oval
tool, Figure 9.
If I were invited to estimate the probable number of the more perfect
tools found in the valley of the Somme since 1842, rejecting all the
knives, and all that might be suspected of being spurious or forged, I
should conjecture that they far exceeded a thousand. Yet it would be
a great mistake to imagine that an antiquary or geologist, who should
devote a few weeks to the exploration of such a valley as that of the
Somme, would himself be able to detect a single specimen. But few tools
were lying on the surface. The rest have been exposed to view by the
removal of such a volume of sand, clay, and gravel, that the price of
the discovery of one of them could only be estimated by knowing how many
hundred labourers have toiled at the fortifications of Abbeville, or
in the sand and gravel pits near that city, and around Amiens, for road
materials and other economic purposes, during the last twenty years.
[Illustration: Figure 15. Fossils of the White Chalk]
(FIGURE 15. FOSSILS OF THE WHITE CHALK.
a, b. Coscinopora globularis, D'Orbigny. Orbitolina concava,
Parker and Jones. c. Part of same magnified.)
In the gravel pits of St. Acheul, and in some others near Amiens, small
round bodies, having a tubular cavity in the centre, occur. They are
well known as fossils of the White Chalk. Dr. Rigollot suggested that
they might have been strung together as beads, and he supposed the hole
in the middle to have been artificial. Some of these round bodies are
found entire in the Chalk and in the gravel, others have naturally a
hole passing through them, and sometimes one or two holes penetrating
some way in from the surface, but not extending to the other side.
Others, like b, Figure 15, have a large cavity, which has a very
artificial aspect. It is impossible to decide whether they have or have
not served as personal ornaments, recommended by their globular form,
lightness, and by being less destructible than ordinary Chalk. Granting
that there were natural cavities in the axis of some of them, it does
not follow that these may not have been taken advantage of for stringing
them as beads, while others may have been artificially bored through.
Dr. Rigollot's argument in favour of their having been used as necklaces
or bracelets, appears to me a sound one. He says he often found small
heaps or groups of them in one place, all perforated, just as if, when
swept into the river's bed by a flood, the bond which had united them
together remained unbroken.*
(* Rigollot, "Memoire sur des Instruments en Silex" etc.,
Amiens 1854 page 16.)