OF THE SOMME--CONCLUDED.
Fluvio-marine Strata, with Flint Implements, near Abbeville.
Marine Shells in same.
Cyrena fluminalis.
Mammalia.
Entire Skeleton of Rhinoceros.
Flint Implements, why found low down in Fluviatile Deposits.
Rivers shifting their Channels.
Relative Ages of higher and lower-level Gravels.
Section of Alluvium of St. Acheul.
Two Species of Elephant and Hippopotamus coexisting with Man
in France.
Volume of Drift, proving Antiquity of Flint Implements.
Absence of Human Bones in tool-bearing Alluvium, how explained.
Value of certain Kinds of negative Evidence tested thereby.
Human Bones not found in drained Lake of Haarlem.
In the section of the valley of the Somme given in Figure 7, the
successive formations newer than the Chalk are numbered in chronological
order, beginning with the most modern, or the peat, which is marked
Number 1, and which has been treated of in the last chapter. Next in the
order of antiquity are the lower-level gravels, Number 2, which we have
now to describe; after which the alluvium, Number 3, found at higher
levels, or about 80 and 100 feet above the river-plain, will remain to
be considered.
I have selected, as illustrating the old alluvium of the Somme occurring
at levels slightly elevated above the present river, the sand and
gravel-pits of Menchecourt, in the northwest suburbs of Abbeville, to
which, as before stated, attention was first drawn by M. Boucher de
Perthes, in his work on Celtic antiquities. Here, although in every
adjoining pit some minor variations in the nature and thickness of the
superimposed deposits may be seen, there is yet a general approach to
uniformity in the series. The only stratum of which the relative age
is somewhat doubtful, is the gravel marked a, underlying the peat, and
resting on the Chalk. It is only known by borings, and some of it may be
of the same age as Number 3; but I believe it to be for the most part
of more modern origin, consisting of the wreck of all the older gravel,
including Number 3, and formed during the last hollowing out and
deepening of the valley immediately before the commencement of the
growth of peat.
The greater number of flint implements have been dug out of Number 3,
often near the bottom, and twenty-five, thirty, or even more than thirty
feet below the surface of Number 1.
A geologist will perceive by a glance at the section that the valley of
the Somme must have been excavated nearly to its present depth and
width when the strata of Number 3 were thrown down, and that after the
deposits Numbers 3, 2, and 1 had been formed in succession, the present
valley was scooped out, patches only of Numbers 3 and 2 being left. For
these deposits cannot originally have ended abruptly as they now do, but
must have once been continuous farther towards the centre of the valley.
[Illustration: Figure 16. Fluvio-Marine Strata]
(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. [16]
[Illustration: Figure 17. Cyrena fluminalis]
(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.
The following marine shells occur mixed with the freshwater species
above enumerated:--Buccinum undatum, Littorina littorea, Nassa
reticulata, Purpura lapillus, Tellina solidula, Cardium edule, and
fragments of some others. Several of these I have myself collected
entire, though in a state of great decomposition, lying in the white
sand called "sable aigre" by the workmen. They are all littoral species
now proper to the contiguous coast of France. Their occurrence in a
fossil state associated with freshwater shells at Menchecourt had been
noticed as long ago as 1836 by MM. Ravin and Baillon, before M. Boucher
de Perthes commenced the researches which have since made the locality
so celebrated.*
(* D'Archiac, "Histoire des Progres" etc. volume 2 page
154.)
The numbers since collected preclude all idea of their having been
brought inland as eatable shells by the fabricators of the flint
hatchets found at the bottom of the fluvio-marine sands. From the same
beds, and in marls alternating with the sands, remains of the elephant,
rhinoceros, and other mammalia have been exhumed.
Above the fluvio-marine strata are those designated Number 2 in the
section (Figure 16), which are almost devoid of stratification, and
probably formed of mud or sediment thrown down by the waters of the
river when they overflowed the ancient alluvial plain of that day. Some
land shells, a few river shells, and bones of mammalia, some of them
extinct, occur in Number 2. Its upper surface has been deeply furrowed
and cut into by the action of water, at the time when the earthy matter
of Number 1 was superimposed. The materials of this uppermost deposit
are arranged as if they had been the result of land floods, taking place
after the formations 2 and 3 had been raised, or had become exposed to
denudation.
The fluvio-marine strata and overlying loam of Menchecourt recur on the
opposite or left bank of the alluvial plain of the Somme, at a distance
of 2 or 3 miles. They are found at Mautort, among other places, and I
obtained there the flint hatchet shown in Figure 9, of an oval form. It
was extracted from gravel, above which were strata containing a mixture
of marine and freshwater shells, precisely like those of Menchecourt.
In the alluvium of all parts of the valley, both at high and low levels,
rolled bones are sometimes met with in the gravel. Some of the flint
tools in the gravel of Abbeville have their angles very perfect, others
have been much triturated, as if in the bed of the main river or some of
its tributaries.
The mammalia most frequently cited as having been found in the deposits
Numbers 2 and 3 at Menchecourt, are the following:--
Elephas primigenius.
Rhinoceros tichorhinus.
Equus fossilis, Owen.
Bos primigenius.
Cervus somonensis, Cuvier.
C. tarandus priscus, Cuvier.
Felis spelaea.
Hyaena spelaea.
The Ursus spelaeus has also been mentioned by some writers; but
M. Lartet says he has sought in vain for it among the osteological
treasures sent from Abbeville to Cuvier at Paris, and in other
collections. The same palaeontologist, after a close scrutiny of the
bones sent formerly to the Paris Museum from the valley of the Somme,
observed that some of them bore the evident marks of an instrument,
agreeing well with incisions such as a rude flint-saw would produce.
Among other bones mentioned as having been thus artificially cut,
are those of a Rhinoceros tichorhinus, and the antlers of Cervus
somonensis.*
(* "Quarterly Journal of the Geological Society" volume 16
1860 page 471.)
The evidence obtained by naturalists that some of the extinct mammalia
of Menchecourt really lived and died in this part of France, at the
time of the embedding of the flint tools in fluviatile strata, is most
satisfactory; and not the less so for having been put on record long
before any suspicion was entertained that works of art would ever be
detected in the same beds. Thus M. Baillon, writing in 1834 to M. Ravin,
says: "They begin to meet with fossil bones at the depth of 10 or 12
feet in the Menchecourt sand-pits, but they find a much greater quantity
at the depth of 18 and 20 feet. Some of them were evidently broken
before they were embedded, others are rounded, having, without doubt,
been rolled by running water. It is at the bottom of the sand-pits that
the most entire bones occur. Here they lie without having undergone
fracture or friction, and seem to have been articulated together at the
time when they were covered up. I found in one place a whole hind limb
of a rhinoceros, the bones of which were still in their true relative
position. They must have been joined together by ligaments, and even
surrounded by muscles at the time of their interment. The entire
skeleton of the same species was lying at a short distance from the
spot."*
(* "Societe Roy. d'Emulation d'Abbeville" 1834 page 197.)
If we suppose that the greater number of the flint implements occurring
in the neighbourhood of Abbeville and Amiens were brought by river
action into their present position, we can at once explain why so large
a proportion of them are found at considerable depths from the surface,
for they would naturally be buried in gravel and not in fine sediment,
or what may be termed "inundation mud," such as Number 2 (Figure 16),
a deposit from tranquil water, or where the stream had not sufficient
force or velocity to sweep along Chalk flints, whether wrought or
unwrought. Hence we have almost always to pass down through a mass of
incumbent loam with land shells, or through fine sand with freshwater
molluscs, before we get into the beds of gravel containing hatchets.
Occasionally a weapon used as a projectile may have fallen into quiet
water, or may have dropped from a canoe to the bottom of the river, or
may have been floated by ice, as are some stones occasionally by the
Thames in severe winters, and carried over the meadows bordering its
banks; but such cases are exceptional, though helping to explain how
isolated flint tools or pebbles and angular stones are now and then to
be seen in the midst of the finest loams.
The endless variety in the sections of the alluvium of the valley of the
Somme, may be ascribed to the frequent silting up of the main stream and
its tributaries during different stages of the excavation of the valley,
probably also during changes in the level of the land. As a rule, when a
river attacks and undermines one bank, it throws down gravel and sand on
the opposite side of its channel, which is growing somewhere shallower,
and is soon destined to be raised so high as to form an addition to
the alluvial plain, and to be only occasionally inundated. In this way,
after much encroachment on cliff or meadow at certain points, we find
at the end of centuries that the width of the channel has not been
enlarged, for the new made ground is raised after a time to the average
height of the older alluvial tract. Sometimes an island is formed in
midstream, the current flowing for a while on both sides of it, and
at length scooping out a deeper channel on one side so as to leave the
other to be gradually filled up during freshets and afterwards elevated
by inundation mud, or "brick-earth." During the levelling up of these
old channels, a flood sometimes cuts into and partially removes portions
of the previously stratified matter, causing those repeated signs of
furrowing and filling up of cavities, those memorials of doing and
undoing, of which the tool-bearing sands and gravels of Abbeville and
Amiens afford such reiterated illustrations, and of which a parallel is
furnished by the ancient alluvium of the Thames valley, where similar
bones of extinct mammalia and shells, including Cyrena fluminalis, are
found.
Professor Noeggerath, of Bonn, informs me that, about the year 1845,
when the bed of the Rhine was deepened artificially by the blasting
and removal of rock in the narrows at Bingerloch, not far from Bingen,
several flint hatchets and an extraordinary number of iron weapons of
the Roman period were brought up by the dredge from the bed of the great
river. The decomposition of the iron had caused much of the gravel to
be cemented together into a conglomerate. In such a case we have only
to suppose the Rhine to deviate slightly from its course, changing
its position, as it has often done in various parts of its plain in
historical times, and then tools of the stone and iron periods would
be found in gravel at the bottom with a great thickness of sand and
overlying loam deposited above them.
Changes in a river plain, such as those above alluded to, give rise
frequently to ponds, swamps, and marshes, marking the course of old beds
or branches of the river not yet filled up, and in these depressions
shells proper both to running and stagnant water may be preserved, and
quadrupeds may be mired. The latest and uppermost deposit of the series
will be loam or brick-earth, with land and amphibious shells (Helix and
Succinea), while below will follow strata containing freshwater shells,
implying continuous submergence; and lowest of all in most sections will
be the coarse gravel accumulated by a current of considerable strength
and velocity.
When the St. Katharine docks were excavated at London, and similar works
executed on the banks of the Mersey, old ships were dug out, as I have
elsewhere noticed,* showing how the Thames and Mersey have in modern
times been shifting their channels.
(* "Principles of Geology" 10th edition volume 2 page 547.)
Recently, an old silted-up bed of the Thames has been discovered by
boring at Shoeburyness at the mouth of the river opposite Sheerness, as
I learn from Mr. Mylne. The old deserted branch is separated from the
new or present channel of the Thames, by a mass of London Clay which
has escaped denudation. The depth of the old branch, or the thickness
of fluviatile strata with which it has been filled up, is 75 feet. The
actual channel in the neighbourhood is now 60 feet deep, but there is
probably 10 or 15 feet of stratified sand and gravel at the bottom; so
that, should the river deviate again from its course, its present bed
might be the receptacle of a fluvio-marine formation 75 feet thick,
equal to the former one of Shoeburyness, and more considerable than that
of Abbeville. It would consist both of freshwater and marine strata,
as the salt water is carried by the tide far up above Sheerness; but in
order that such deposits should resemble, in geological position, the
Menchecourt beds, they must be raised 10 or 15 feet above their present
level, and be partially eroded. Such erosion they would not fail to
suffer during the process of upheaval, because the Thames would scour
out its bed, and not alter its position relatively to the sea, while the
land was gradually rising.
Before the canal was made at Abbeville, the tide was perceptible in
the Somme for some distance above that city. It would only require,
therefore, a slight subsidence to allow the salt water to reach
Menchecourt, as it did in the Pleistocene period. As a stratum
containing exclusively land and freshwater shells usually underlies
the fluvio-marine sands at Menchecourt, it seems that the river first
prevailed there, after which the land subsided; and then there was an
upheaval which raised the country to a greater height than that at which
it now stands, after which there was a second sinking, indicated by the
position of the peat, as already explained. All these changes happened
since Man first inhabited this region.
At several places in the environs of Abbeville there are fluviatile
deposits at a higher level by 50 feet than the uppermost beds at
Menchecourt, resting in like manner on the Chalk. One of these occurs in
the suburbs of the city at Moulin Quignon, 100 feet above the Somme
and on the same side of the valley as Menchecourt, and containing flint
implements of the same antique type and the bones of elephants; but no
marine shells have been found there, nor in any gravel or sand at higher
elevations than the Menchecourt marine shells.
It has been a matter of discussion among geologists whether the higher
or the lower sands and gravels of the Somme valley are the more ancient.
As a general rule, when there are alluvial formations of different ages
in the same valley, those which occupy a more elevated position above
the river plain are the oldest. In Auvergne and Velay, in Central
France, where the bones of fossil quadrupeds occur at all heights above
the present rivers from 10 to 1000 feet, we observe the terrestrial
fauna to depart in character from that now living in proportion as
we ascend to higher terraces and platforms. We pass from the lower
alluvium, containing the mammoth, tichorhine rhinoceros, and reindeer,
to various older groups of fossils, till, on a tableland 1000 feet high
(near Le Puy, for example), the abrupt termination of which overlooks
the present valley, we discover an old extinct river-bed covered by
a current of ancient lava, showing where the lowest level was once
situated. In that elevated alluvium the remains of a Tertiary mastodon
and other quadrupeds of like antiquity are embedded.
If the Menchecourt beds had been first formed, and the valley, after
being nearly as deep and wide as it is now, had subsided, the sea
must have advanced inland, causing small delta-like accumulations at
successive heights, wherever the main river and its tributaries met
the sea. Such a movement, especially if it were intermittent, and
interrupted occasionally by long pauses, would very well account for the
accumulation of stratified debris which we encounter at certain points
in the valley, especially around Abbeville and Amiens. But we are
precluded from adopting this theory by the entire absence of marine
shells, and the presence of freshwater and land species, and mammalian
bones, in considerable abundance, in the drift both of higher and lower
levels above Abbeville. Had there been a total absence of all organic
remains, we might have imagined the former presence of the sea, and the
destruction of such remains might have been ascribed to carbonic acid
or other decomposing causes; but the Pleistocene and implement-bearing
strata can be shown by their fossils to be of fluviatile origin.
FLINT IMPLEMENTS IN GRAVEL NEAR AMIENS. GRAVEL OF ST. ACHEUL.
When we ascend the valley of the Somme, from Abbeville to Amiens, a
distance of about 25 miles, we observe a repetition of all the same
alluvial phenomena which we have seen exhibited at Menchecourt and its
neighbourhood, with the single exception of the absence of marine shells
and of Cyrena fluminalis. We find lower-level gravel, such as Number 2,
Figure 7, and higher-level alluvium, such as Number 3, the latter rising
to 100 feet above the plain, which at Amiens is about 50 feet above the
level of the river at Abbeville. In both the upper and lower gravels,
as Dr. Rigollot stated in 1854, flint tools and the bones of extinct
animals, together with river shells and land shells of living species,
abound.
[Illustration: Figures 18, 19 and 20. Elephas]
(FIGURE 18.* Elephas primigenius.
Penultimate molar, lower jaw, right side, one-third of
natural size, Pleistocene. Co-existed with Man.)
(FIGURE 19.* Elephas antiquus, Falconer.
Penultimate molar, lower jaw, right side, one-third of natural
size, Pleistocene and Newer Pliocene. Co-existed with Man.)
(FIGURE 20.* Elephas meridionalis, Nesti.
Penultimate molar, lower jaw, right side, one-third of natural
size, Newer Pliocene, Saint Prest, near Chartres, and
Norwich Crag. Not yet proved to have coexisted with Man.)
(* For Figure 20 I am indebted to M. Lartet, and Figure 18
will be found in his paper in "Bulletin de la Societe
Geologique de France" March 1859. Figure 19 is from Falconer
and Cautley "Fauna Sivalensis.")
Immediately below Amiens, a great mass of stratified gravel, slightly
elevated above the alluvial plain of the Somme, is seen at St. Roch,
and half a mile farther down the valley at Montiers. Between these two
places a small tributary stream, called the Celle, joins the Somme. In
the gravel at Montiers, Mr. Prestwich and I found some flint knives, one
of them flat on one side, but the other carefully worked, and exhibiting
many fractures, clearly produced by blows skilfully applied. Some of
these knives were taken from so low a level as to satisfy us that this
great bed of gravel at Montiers, as well as that of the contiguous
quarries of St. Roch, which seems to be a continuation of the same
deposit, may be referred to the human period. Dr. Rigollot had already
mentioned flint hatchets as obtained by him from St. Roch, but as
none have been found there of late years, his statement was thought to
require confirmation. The discovery, therefore, of these flint knives
in gravel of the same age was interesting, especially as many tusks of
a hippopotamus have been obtained from the gravel of St. Roch--some of
these recently by Mr. Prestwich; while M. Garnier of Amiens has procured
a fine elephant's molar from the same pits, which Dr. Falconer refers to
Elephas antiquus, see Figure 19. Hence I infer that both these animals
co-existed with Man.
The alluvial formations of Montiers are very instructive in another
point of view. If, leaving the lower gravel of that place, which is
topped with loam or brick-earth (of which the upper portion is about
30 feet above the level of the Somme), we ascend the Chalk slope to
the height of about 80 feet, another deposit of gravel and sand, with
fluviatile shells in a perfect condition, occurs, indicating most
clearly an ancient river-bed, the waters of which ran habitually at
that higher level before the valley had been scooped out to its present
depth. This superior deposit is on the same side of the Somme, and about
as high, as the lowest part of the celebrated formation of St. Acheul, 2
or 3 miles distant, to which I shall now allude.
The terrace of St. Acheul may be described as a gently sloping ledge of
Chalk, covered with gravel, topped as usual with loam or fine sediment,
the surface of the loam being 100 feet above the Somme, and about 150
above the sea.
Many stone coffins of the Gallo-Roman period have been dug out of the
upper portion of this alluvial mass. The trenches made for burying
them sometimes penetrate to the depth of 8 or 9 feet from the surface,
entering the upper part of Number 3 of the sections Figures 21 and 22.
They prove that when the Romans were in Gaul they found this terrace in
the same condition as it is now, or rather as it was before the removal
of so much gravel, sand, clay, and loam, for repairing roads, and for
making bricks and pottery.
[Illustration: Figure 21. Section of Gravel Pit]
(FIGURE 21. SECTION OF GRAVEL PIT CONTAINING FLINT IMPLEMENTS
AT ST. ACHEUL, NEAR AMIENS, OBSERVED IN JULY 1860.
1. Vegetable soil and made ground, 2 to 3 feet thick.
2. Brown loam with some angular flints, in parts passing into
ochreous gravel, filling up indentations on the surface
of Number 3, 3 feet thick.
3. White siliceous sand with layers of chalky marl, and included
fragments of Chalk, for the most part unstratified, 9 feet.
4. Flint-gravel, and whitish chalky sand, flints subangular,
average size of fragments, 3 inches diameter, but with some
large unbroken Chalk flints intermixed, cross stratification
in parts. Bones of mammalia, grinder of elephant at b, and
flint implement at c, 10 to 14 feet.
5. Chalk with flints.
a. Part of elephant's molar, 11 feet from the surface.
b. Entire molar of Elephas primigenius, 17 feet from the surface.
c. Position of flint hatchet, 18 feet from the surface.)
In the annexed section (Figure 21), which I observed during my last
visit in 1860, it will be seen that a fragment of an elephant's tooth is
noticed as having been dug out of unstratified sandy loam at the point
a, 11 feet from the surface. This was found at the time of my visit; and
at a lower point, at b, 18 feet from the surface, a large nearly entire
and unrolled molar of the same species was obtained, which is now in my
possession. It has been pronounced by Dr. Falconer to belong to Elephas
primigenius.
A stone hatchet of an oval form, like that represented at Figure 9, was
discovered at the same time, about one foot lower down, at c, in densely
compressed gravel. The surface of the fundamental Chalk is uneven
in this pit, and slopes towards the valley-plain of the Somme. In a
horizontal distance of 20 feet, I found a difference in vertical height
of 7 feet. In the chalky sand, sometimes occurring in interstices
between the separate fragments of flint, constituting the coarse gravel
Number 4, entire as well as broken freshwater shells are often met with.
To some it may appear enigmatical how such fragile objects could have
escaped annihilation in a river-bed, when flint tools and much gravel
were shoved along the bottom; but I have seen the dredging instrument
employed in the Thames, above and below London Bridge, to deepen the
river, and worked by steam power, scoop up gravel and sand from the
bottom, and then pour the contents pell-mell into the boat, and still
many specimens of Limnaea, Planorbis, Paludina, Cyclas, and other shells
might be taken out uninjured from the gravel.
It will be observed that the gravel Number 4 is obliquely stratified,
and that its surface had undergone denudation before the white sandy
loam Number 3 was superimposed. The materials of the gravel at d must
have been cemented or frozen together into a somewhat coherent mass
to allow the projecting ridge, d, to stand up 5 feet above the general
surface, the sides being in some places perpendicular. In Number 3 we
probably behold an example of a passage from river-silt to inundation
mud. In some parts of it, land shells occur.
It has been ascertained by MM. Buteux, Ravin, and other observers
conversant with the geology of this part of France, that in none of the
alluvial deposits, ancient or modern, are there any fragments of rocks
foreign to the basin of the Somme--no erratics which could only be
explained by supposing them to have been brought by ice, during a
general submergence of the country, from some other hydrographical
basin.
But in some of the pits at St. Acheul there are seen in the beds Number
4, Figure 21, not only well-rounded Tertiary pebbles, but great
blocks of hard sandstone, of the kind called in the south of England
"greywethers," some of which are 3 or 4 feet and upwards in diameter.
They are usually angular, and when spherical owe their shape generally
to an original concretionary structure, and not to trituration in a
river's bed. These large fragments of stone abound both in the higher
and lower level gravels round Amiens and at the higher level at
Abbeville. They have also been traced far up the valley above Amiens,
wherever patches of the old alluvium occur. They have all been derived
from the Tertiary strata which once covered the Chalk. Their dimensions
are such that it is impossible to imagine a river like the present
Somme, flowing through a flat country, with a gentle fall towards
the sea, to have carried them for miles down its channel unless ice
co-operated as a transporting power. Their angularity also favours the
supposition of their having been floated by ice, or rendered so
buoyant by it as to have escaped much of the wear and tear which blocks
propelled along the bottom of a river channel would otherwise suffer.
We must remember that the present mildness of the winters in Picardy
and the northwest of Europe generally is exceptional in the northern
hemisphere, and that large fragments of granite, sandstone, and
limestone are now carried annually by ice down the Canadian rivers in
latitudes farther south than Paris.*
(* "Principles of Geology" 9th edition page 220.)
[Illustration: Figure 22. Contorted Strata]
(FIGURE 22. CONTORTED FLUVIATILE STRATA AT ST. ACHEUL
(Prestwich, "Philosophical Transactions" 1861, page 299).
1. Surface soil.
2. Brown loam as in Figure 21, thickness, 6 feet.
3. White sand with bent and folded layers of marl, thickness,
6 feet.
4. Gravel, as in Figure 21, with bones of mammalia and flint
implements.
A. Graves filled with made ground and human bones.
b and c. Seams of laminated marl often bent round upon themselves.
d. Beds of gravel with sharp curves.)
Another sign of ice agency, of which Mr. Prestwich has given a good
illustration in one of his published sections, and which I myself
observed in several pits at St. Acheul, deserves notice. It consists
in flexures and contortions of the strata of sand, marl, and gravel (as
seen at b, c, and d, Figure 22), which they have evidently undergone
since their original deposition, and from which both the underlying
Chalk and part of the overlying beds of sand Number 3 are usually
exempt.
In my former writings I have attributed this kind of derangement to two
causes; first, the pressure of ice running aground on yielding banks of
mud and sand; and, secondly, the melting of masses of ice and snow of
unequal thickness, on which horizontal layers of mud, sand, and other
fine and coarse materials had accumulated. The late Mr. Trimmer first
pointed out in what manner the unequal failure of support caused by the
liquefaction of underlying or intercalated snow and ice might give rise
to such complicated foldings.*
(* See chapter 12.)
When "ice-jams" occur on the St. Lawrence and other Canadian rivers
(latitude 46 degrees north), the sheets of ice, which become packed or
forced under or over one another, assume in most cases a highly inclined
and sometimes even a vertical position. They are often observed to be
coated on one side with mud, sand, or gravel frozen on to them, derived
from shallows in the river on which they rested when congelation first
reached the bottom.
As often as portions of these packs melt near the margin of the
river, the layers of mud, sand, and gravel, which result from their
liquefaction, cannot fail to assume a very abnormal arrangement--very
perplexing to a geologist who should undertake to interpret them without
having the ice-clue in his mind.
Mr. Prestwich has suggested that ground-ice may have had its influence
in modifying the ancient alluvium of the Somme.*
(* Prestwich, Memoir read to Royal Society, April 1862.)
It is certain that ice in this form plays an active part every winter
in giving motion to stones and gravel in the beds of rivers in European
Russia and Siberia. It appears that when in those countries the streams
are reduced nearly to the freezing point, congelation begins frequently
at the bottom; the reason being, according to Arago, that the current is
slowest there, and the gravel and large stones, having parted with much
of their heat by radiation, acquire a temperature below the average of
the main body of the river. It is, therefore, when the water is clear,
and the sky free from clouds, that ground ice forms most readily, and
oftener on pebbly than on muddy bottoms. Fragments of such ice, rising
occasionally to the surface, bring up with them gravel, and even large
stones.
Without dwelling longer on the various ways in which ice may affect the
forms of stratification in drift, so as to cause bendings and foldings
in which the underlying or over-lying strata do not participate, a
subject to which I shall have occasion again to allude in the sequel,
I will state in this place that such contortions, whether explicable or
not, are very characteristic of glacial formations. They have also no
necessary connection with the transportation of large blocks of stone,
and they therefore afford, as Mr. Prestwich remarks, independent proof
of ice-action in the Pleistocene gravel of the Somme.
Let us, then, suppose that, at the time when flint hatchets were
embedded in great numbers in the ancient gravel which now forms the
terrace of St. Acheul, the main river and its tributaries were annually
frozen over for several months in winter. In that case, the primitive
people may, as Mr. Prestwich hints, have resembled in their mode of life
those American Indians who now inhabit the country between Hudson's Bay
and the Polar Sea. The habits of those Indians have been well described
by Hearne, who spent some years among them. As often as deer and other
game become scarce on the land, they betake themselves to fishing in
the rivers; and for this purpose, and also to obtain water for drinking,
they are in the constant practice of cutting round holes in the ice, a
foot or more in diameter, through which they throw baited hooks or nets.
Often they pitch their tent on the ice, and then cut such holes through
it, using ice-chisels of metal when they can get copper or iron, but
when not, employing tools of flint or hornstone.
The great accumulation of gravel at St. Acheul has taken place in part
of the valley where the tributary streams, the Noye and the Arve, now
join the Somme. These tributaries, as well as the main river, must have
been running at the height first of 100 feet, and afterwards at various
lower levels above the present valley-plain, in those earlier times
when the flint tools of the antique type were buried in successive river
beds. I have said at various levels, because there are, here and there,
patches of drift at heights intermediate between the higher and lower
gravel, and also some deposits, showing that the river once flowed
at elevations above as well as below the level of the platform of St.
Acheul. As yet, however, no patch of gravel skirting the valley at
heights exceeding 100 feet above the Somme has yielded flint tools or
other signs of the former sojourn of Man in this region.
Possibly, in the earlier geographical condition of this country, the
confluence of tributaries with the Somme afforded inducements to a
hunting and fishing tribe to settle there, and some of the same natural
advantages may have caused the first inhabitants of Amiens and Abbeville
to fix on the same sites for their dwellings. If the early hunting and
fishing tribes frequented the same spots for hundreds or thousands of
years in succession, the number of the stone implements lost in the
bed of the river need not surprise us. Ice-chisels, flint hatchets, and
spear-heads may have slipped accidentally through holes kept constantly
open, and the recovery of a lost treasure once sunk in the bed of the
ice-bound stream, inevitably swept away with gravel on the breaking up
of the ice in the spring, would be hopeless. During a long winter, in a
country affording abundance of flint, the manufacture of tools would be
continually in progress; and, if so, thousands of chips and flakes
would be purposely thrown into the ice-hole, besides a great number of
implements having flaws, or rejected as too unskilfully made to be worth
preserving.
As to the fossil fauna of the drift, considered in relation to the
climate, when, in 1859, I took a collection which I had made of all the
more common species of land and freshwater shells from the Amiens and
Abbeville drift, to my friend M. Deshayes at Paris, he declared them to
be, without exception, the same as those now living in the basin of the
Seine. This fact may seem at first sight to imply that the climate had
not altered since the flint tools were fabricated; but it appears that
all these species of molluscs now range as far north as Norway and
Finland, and may therefore have flourished in the valley of the Somme
when the river was frozen over annually in winter.*
(* See Prestwich, Paper read to the Royal Society in 1862.)
In regard to the accompanying mammalia, some of them, like the mammoth
and tichorhine rhinoceros, may have been able to endure the rigours of
a northern winter as well as the reindeer, which we find fossil in
the same gravel. It is a more difficult point to determine whether the
climate of the lower gravels (those of Menchecourt, for example) was
more genial than that of the higher ones. Mr. Prestwich inclines to this
opinion. None of those contortions of the strata above described have
as yet been observed in the lower drift. It contains large blocks of
Tertiary sandstone and grit, which may have required the aid of ice to
convey them to their present sites; but as such blocks already abounded
in the older and higher alluvium, they may simply be monuments of its
destruction, having been let down successively to lower and lower levels
without making much seaward progress.
The Cyrena fluminalis of Menchecourt and the hippopotamus of St. Roch
seem to be in favour of a less severe temperature in winter; but so
many of the species of mammalia, as well as of the land and freshwater
shells, are common to both formations, and our information respecting
the entire fauna is still so imperfect, that it would be premature to
pretend to settle this question in the present state of our knowledge.
We must be content with the conclusion (and it is one of no small
interest), that when Man first inhabited this part of Europe, at the
time that the St. Acheul drift was formed, the climate as well as the
physical geography of the country differed considerably from the state
of things now established there.
Among the elephant remains from St. Acheul, in M. Garnier's collection,
Dr. Falconer recognised a molar of the Elephas antiquus, Figure 19, the
same species which has been already mentioned as having been found in
the lower-level gravels of St. Roch. This species, therefore, endured
while important changes took place in the geographical condition of the
valley of the Somme. Assuming the lower-level gravel to be the newer,
it follows that the Elephas antiquus and the hippopotamus of St. Roch
continued to flourish long after the introduction of the mammoth, a
well characterised tooth of which, as I before stated, was found at St.
Acheul at the time of my visit in 1860.
As flint hatchets and knives have been discovered in the alluvial
deposits both at high and low levels, we may safely affirm that Man was
as old an inhabitant of this region as were any of the fossil quadrupeds
above enumerated, a conclusion which is independent of any difference of
opinion as to the relative age of the higher and lower gravels.
The disappearance of many large pachyderms and beasts of prey from
Europe has often been attributed to the intervention of Man, and no
doubt he played his part in hastening the era of their extinction; but
there is good reason for suspecting that other causes co-operated to
the same end. No naturalist would for a moment suppose that the
extermination of the Cyrena fluminalis throughout the whole of Europe--a
species which co-existed with our race in the valley of the Somme, and
which was very abundant in the waters of the Thames at the time when
the elephant, rhinoceros, and hippopotamus flourished on its banks--was
accelerated by human agency. The great modification in climate and in
other conditions of existence which affected this aquatic mollusc, may
have mainly contributed to the gradual dying out of many of the large
mammalia.
We have already seen that the peat of the valley of the Somme is a
formation which, in all likelihood, took thousands of years for
its growth. But no change of a marked character has occurred in the
mammalian fauna since it began to accumulate. The contrast of the fauna
of the ancient alluvium, whether at high or low levels, with the fauna
of the oldest peat is almost as great as its contrast with the existing
fauna, the memorials of Man being common to the whole series; hence we
may infer that the interval of time which separated the era of the
large extinct mammalia from that of the earliest peat, was of far longer
duration than that of the entire growth of the peat. Yet we by no means
need the evidence of the ancient fossil fauna to establish the antiquity
of Man in this part of France. The mere volume of the drift at various
heights would alone suffice to demonstrate a vast lapse of time during
which such heaps of shingle, derived both from the Eocene and the
Cretaceous rocks, were thrown down in a succession of river-channels. We
observe thousands of rounded and half-rounded flints, and a vast number
of angular ones, with rounded pieces of white Chalk of various sizes,
testifying to a prodigious amount of mechanical action, accompanying
the repeated widening and deepening of the valley, before it became the
receptacle of peat; and the position of many of the flint tools leaves
no doubt in the mind of the geologist that their fabrication preceded
all this reiterated denudation.
ON THE ABSENCE OF HUMAN BONES IN THE ALLUVIUM OF THE SOMME.
It is naturally a matter of no small surprise that, after we have
collected many hundred flint implements (including knives, many
thousands), not a single human bone has yet been met with in the old
alluvial sand and gravel of the Somme. This dearth of the mortal remains
of our species holds true equally, as yet, in all other parts of
Europe where the tool-bearing drift of the Pleistocene period has been
investigated in valley deposits. Yet in these same formations there is
no want of bones of mammalia belonging to extinct and living species. In
the course of the last quarter of a century, thousands of them have been
submitted to the examination of skilful osteologists, and they have been
unable to detect among them one fragment of a human skeleton, not even
a tooth. Yet Cuvier pointed out long ago, that the bones of Man found
buried in ancient battle-fields were not more decayed than those of
horses interred in the same graves. We have seen that in the Liege
caverns, the skulls, jaws, and teeth, with other bones of the human
race, were preserved in the same condition as those of the cave-bear,
tiger, and mammoth.
That ere long, now that curiosity has been so much excited on this
subject, some human remains will be detected in the older alluvium of
European valleys, I confidently expect. In the meantime, the absence of
all vestige of the bones which belonged to that population by which so
many weapons were designed and executed, affords a most striking and
instructive lesson in regard to the value of negative evidence, when
adduced in proof of the non-existence of certain classes of terrestrial
animals at given periods of the past. It is a new and emphatic
illustration of the extreme imperfection of the geological record, of
which even they who are constantly working in the field cannot easily
form a just conception.
We must not forget that Dr. Schmerling, after finding extinct mammalia
and FLINT TOOLS in forty-two Belgian caverns, was only rewarded by the
discovery of human bones in three or four of those rich repositories of
osseous remains. In like manner, it was not till the year 1855 that
the first skull of the musk ox (Bubalus moschatus) was detected in the
fossiliferous gravel of the Thames, and not till 1860, as will be
seen in the next chapter, that the same quadruped was proved to have
co-existed in France with the mammoth. The same theory which will
explain the comparative rarity of such species would no doubt account
for the still greater scarcity of human bones, as well as for our
general ignorance of the Pleistocene terrestrial fauna, with the
exception of that part of it which is revealed to us by cavern
researches.
In valley drift we meet commonly with the bones of quadrupeds which
graze on plains bordering rivers. Carnivorous beasts, attracted to the
same ground in search of their prey, sometimes leave their remains
in the same deposits, but more rarely. The whole assemblage of fossil
quadrupeds at present obtained from the alluvium of Picardy is obviously
a mere fraction of the entire fauna which flourished contemporaneously
with the primitive people by whom the flint hatchets were made.
Instead of its being part of the plan of nature to store up enduring
records of a large number of the individual plants and animals which
have lived on the surface, it seems to be her chief care to provide the
means of disencumbering the habitable areas lying above and below the
waters of those myriads of solid skeletons of animals, and those massive
trunks of trees, which would otherwise soon choke up every river, and
fill every valley. To prevent this inconvenience she employs the heat
and moisture of the sun and atmosphere, the dissolving power of carbonic
and other acids, the grinding teeth and gastric juices of quadrupeds,
birds, reptiles, and fish, and the agency of many of the invertebrata.
We are all familiar with the efficacy of these and other causes on the
land; and as to the bottoms of seas, we have only to read the published
reports of Mr. MacAndrew, the late Edward Forbes, and other experienced
dredgers, who, while they failed utterly in drawing up from the deep a
single human bone, declared that they scarcely ever met with a work
of art even after counting tens of thousands of shells and zoophytes,
collected on a coast line of several hundred miles in extent, where
they often approached within less than half a mile of a land peopled by
millions of human beings.
LAKE OF HAARLEM.
It is not many years since the Government of Holland resolved to lay dry
that great sheet of water formerly called the Lake of Haarlem, extending
over 45,000 acres. They succeeded, in 1853, in turning it into dry land,
by means of powerful pumps constantly worked by steam, which raised the
water and discharged it into a canal running for 20 or 30 miles round
the newly-gained land. This land was depressed 13 feet beneath the mean
level of the ocean. I travelled, in 1859, over part of the bed of this
old lake, and found it already converted into arable land, and peopled
by an agricultural population of 5000 souls. Mr. Staring, who had
been for some years employed by the Dutch Government in constructing a
geological map of Holland, was my companion and guide. He informed me
that he and his associates had searched in vain for human bones in the
deposits which had constituted for three centuries the bed of the great
lake.
There had been many a shipwreck, and many a naval fight in those waters,
and hundreds of Dutch and Spanish soldiers and sailors had met there
with a watery grave. The population which lived on the borders of this
ancient sheet of water numbered between thirty and forty thousand souls.
In digging the great canal, a fine section had been laid open, about 30
miles long, of the deposits which formed the ancient bottom of the lake.
Trenches, also, innumerable, several feet deep, had been freshly dug on
all the farms, and their united length must have amounted to thousands
of miles. In some of the sandy soil recently thrown out of the trenches,
I observed specimens of freshwater and brackish-water shells, such as
Unio and Dreissena, of living species; and in clay brought up from below
the sand, shells of Tellina, Lutraria, and Cardium, all of species now
inhabiting the adjoining sea.
As the Dreissena is believed by conchologists to have been introduced
into Western Europe in very modern times, brought with foreign timber
in the holds of vessels from the rivers flowing into the Black Sea, the
layer of sand containing it in the Haarlem lake is probably not more
than a hundred years old.
One or two wrecked Spanish vessels, and arms of the same period, have
rewarded the antiquaries who had been watching the draining operations
in the hope of a richer harvest, and who were not a little disappointed
at the result. In a peaty tract on the margin of one part of the lake a
few coins were dug up; but if history had been silent, and if there had
been a controversy whether Man was already a denizen of this planet
at the time when the area of the Haarlem lake was under water, the
archaeologist, in order to answer this question, must have appealed,
as in the case of the valley of the Somme, not to fossil bones, but to
works of art embedded in the superficial strata.
Mr. Staring, in his valuable memoir on the "Geological Map of Holland,"
has attributed the general scarcity of human bones in Dutch peat,
notwithstanding the many works of art preserved in it, to the power of
the humic and sulphuric acids to dissolve bones, the peat in question
being plentifully impregnated with such acids. His theory may be
correct, but it is not applicable to the gravel of the valley of the
Somme, in which the bones of fossil mammalia are frequent, nor to the
uppermost freshwater strata forming the bottom of a large part of the
Haarlem Lake, in which it is not pretended that such acids occur.
The primitive inhabitants of the valley of the Somme may have been too
wary and sagacious to be often surprised and drowned by floods, which
swept away many an incautious elephant or rhinoceros, horse and ox. But
even if those rude hunters had cherished a superstitious veneration for
the Somme, and had regarded it as a sacred river (as the modern Hindoos
revere the Ganges), and had been in the habit of committing the bodies
of their dead or dying to its waters--even had such funeral rites
prevailed, it by no means follows that the bones of many individuals
would have been preserved to our time.
A corpse cast into the stream first sinks, and must then be almost
immediately overspread with sediment of a certain weight, or it will
rise again when distended with gases, and float perhaps to the sea
before it sinks again. It may then be attacked by fish of marine
species, some of which are capable of digesting bones. If, before being
carried into the sea and devoured, it is enveloped with fluviatile mud
and sand, the next flood, if it lie in mid-channel, may tear it out
again, scatter all the bones, roll some of them into pebbles, and
leave others exposed to destroying agencies; and this may be repeated
annually, till all vestiges of the skeleton may disappear. On the other
hand, a bone washed through a rent into a subterranean cavity, even
though a rarer contingency, may have a greater chance of escaping
destruction, especially if there be stalactite dropping from the roof of
the cave or walls of a rent, and if the cave be not constantly traversed
by too strong a current of engulfed water.