Geological History of the English Channel

vol. cx, part 1] w. B. R. KING ON THE ENGLISH CHANNEL 77
THE GEOLOGICAL HISTORY OF THE ENGLISH CHANNEL
BY PROFESSOR WILLIAM BERNARD ROBINSON KING, O.B.E.M.C. SC.D.F.R.S.
PRESIDENT
ANNIVERSARY ADDRESS DELIVERED AT THE ANNUAL GENERAL MEETING
OF THE SOCIETY ON 28 APRIL, 1954
[PLATE IV]
SUMMARY
The geology of the English Channel has long been known to be much more complex
than might appear from a study of the land areas on either side. The most important
work on the subject was that of Dangeard, who examined a number of dredge
samples and published his results in 1929. In recent years investigations with a
free-drop cover which collected samples of rock in place, and geophysical work,
largely that of Dr. M. N. Hill, have added much new information.
The data now available are brought together and analysed. Maps showing the
areas where each major rock group occurs at surface or at depth and estimates
of thicknesses have been prepared. From these a map of the outcrops under the
Channel and a contour map of the sub-New Red Sandstone-Mesozoic surface (the
so-called Palaeozoic floor) have been drawn.
The history of the area is then reviewed and it is concluded that since the Armorican
orogeny the Channel has been an area with a tendency to intermittent downwarps
while the surrounding land areas cf Devon and Cornwall on the one hand and Brittany
on the other have been areas with intermittent uplift. This leads to the conclusion
that many of the present uplands of Palaeozoic rock were blocked out in early times
and that the present edges of these areas are not far from the positions they have
occupied since New Red Sandstone times. It is suggested that palaeogeographieal
maps of the Mesozoic in this region should show a number of islands rather than a
single landmass in the Western Approaches that includes on its eastern margin many
of the present Palaeozoic land areas ; and that the seas which separate these uplands
are floored with Mesozoic rocks.
A FIRST glance at the geological map of southern England and northern
France suggests that it would be a simple matter to predict the geology of
the area covered by the sea of the English Channel. Clearly one would
expect that in the eastern parts the rocks forming the sea bed would be
Cretaceous with patches of Tertiary ; that between Normandy and Dorset
the Jurassic outcrops would join up without serious difficulty ; and that in
the western Channel the floor of the sea would be formed of large granitic
intrusions and sediments in various stages of metamorphism belonging to
the old Armorican massif. For many years it has been known that this
is by far too simplified a view. My interest in the geology of the Channel
floor was first aroused when our former President, Dr. Lees, asked me in
June 1942 for a report on the rocks forming the sea bed between the Isle of
Wight and Cherbourg on the one hand, and between Dungeness and
Boulogne on the other. He was then working with the Petroleum Division
of the Ministry of Supply and I was geologist with H.Q. 21 Army
Group. It was the early days of the planning of " Pluto," the Pipe-Line
Under The Ocean, and clearly it was important to have as much knowledge
as possible of the state of the bottom upon which the pipe-line would rest.
It was soon found that the amount of accurate information available
was extremely scanty, but that some reasonable guesses might be made, at
any rate so far as the eastern Channel was concerned, by extrapolating
the known tectonic structures of the English and French coastal areas.
Universitesi on March 8, 2016
at Orta Dogu Teknikhttp://jgslegacy.lyellcollection.org/Downloaded from

78 w.B.R. KIN(~ ON THE [VO1. CX,
Besides this speculative method there was the positive evidence from a
certain number of dredging samples obtained by the Pourquoi-pas ? and
described in great detail by L. Dangeard (now Professor at Caen) in the
Annales de l'Institut Ocdanographique. In this work Dangeard gives
reasons for interpreting certain materials fetched up in the dredge as
" rock-in-place " and recent work with the " free-drop " corer has in most
cases confirmed his records.
Apart from Dangeard's very scattered dredgings and the detailed work
in the Straits of Dover, m~nly done in connexion with Channel Tunnel
projects, there was little direct evidence in the eastern area, while in the
western Channel we had, in addition to Dangeard's work, the records made
many years ago by Crawshay, Hunt and Worth of rocks dredged up by
fishermen and the research vessels of the Marine Biological Association
based on Plymouth ; but these deM only with a relatively small area south
of the Eddystone lighthouse.
This was the state of affairs when in 1948 I was rash enough to read a
paper to this Society on the geology of the eastern part of the Channel
(King 1949). It may be as well to summarize the basis on which the map
then given was constructed.
The anticlinal and synclinal axes on both the French and English sides
were studied and the positions of the outcrops in those areas were drawn
as they would appear on a plane surface 100 feet (or 30 metres) below sea-
level. The probable positions of the axes were then projected over the
area covered by the sea, bearing in mind the marked echelon arrange-
ment which is so well seen in the Mesozoic rocks of both the French and
English coastal regions. It was considered that provided the under-
water stratigraphy was similar to that on the adjacent land areas there was
every reason to expect the outcrops to run in the manner indicated on the
map. The few records from Dangeard's work agreed well with this inter-
pretation so far as the main eastern part was concerned. Since that date
no work of a geological nature has been carried out in this part of the area
and in the maps accompanying this Address the lines given in 1948 have
been retained.
In the central and western parts of the Channel, however, considerable
further work has been done. It has been carried out in conjunction with
Dr. M. N. Hill of the Department of Geophysics at Cambridge and has
consisted of seismic geophysical refraction shooting, together with the
taking of samples of the rock floor of the sea with a development of the
Stetson " free-drop " corer. By working in close co-operation with Dr.
Hill it has been possible to interpret the geophysical data in terms of
geology. Some of the results obtained have already been published.
The results obtained with the " free-drop " corer have in the majority
of cases confirmed and amplified the information obtained by Dangeard
and others but have shown, as might be expected, that there are compli-
cations in the geology which were not clear from the earlier records. An
adjustment is, however, necessary in the interpretation of one of
Dangeard's dredge records which has been accepted by the French
geologists and incorporated in their 1 : 1,000,000 map of France (NW.
sheet). In mid-Channel, between the Isle of Wight and Cherbourg, the
presence of New Red Sandstone (Lower Trias) is recorded. When
Dangeard obtained his specimens (No. 395) no other samples were known
from the neighbourhood and naturally, soft, red, friable, clay-like chips
were interpreted as " probably Trias " and were accepted as such for my
1948 map. This area has received most attention during our coring work,

part 1] ENGLISH CHANNEL 79
for clearly it is of great importance in the interpretation of this critical
part of the Channel.
The coring north of Dangeard's station 395 has shown that the inter-
pretation given by me in 1948 was wrong, and that the supposed Trias
found during the reconnaissance for the " Pluto " pipe-line was in reality
red-brown Wealden clays. These are proved by fossil evidence and the
Wealden has been shown to be followed to the south by Purbeck, Portland
and Kimeridge strata. South of the Kimeridge clays Chalk was proved,
and a few miles south of that, in the neighbourhood of Dangeard's station,
grey and mottled clays and silts were obtained but no sign of any rock that
could be interpreted as Trias. Fortunately, samples of Dangeard's dredg-
ings are preserved at Rennes University, and through the kind offices of
Professor Milon I have been able to re-examine some of them.
The material is described by Dangeard (1929, p. 80) as follows :--
Argiles rouges tachant les doigts, tr~s friables, paraissant bien arrach~es en place,
contenant de petits grains de quartz rares, et de petites paillettes micac~es. Un petit
fragment de calcaire fin rouge~tre; quelques moreeaux de calcite. Les argiles
ressemblent beaucoup ~ certaines argiles rouges aflteurant au Plessis (Manche).
The critical fragments are clearly the " argiles rouges "; they certainly
mark the fingers, but not as a red clay does ; they stain rather in the way
a soft haematite or similar iron oxide does and the colour is much more in
keeping with a pure iron oxide than that usually seen in Triassic deposits.
Professor Tilley has kindly examined one specimen and reports : " I
have had an Fe203 determination made. Soluble in HC1 and determined
as Fe208 ~ 22-2~. Insoluble in hot HC1 68% . . . I think the material
is a ferruginized sediment of some kind." Dangeard's specimens therefore
appear to be more like highly weathered iron-ore deposits or lateritic nod-
ules than Trias material, and moreover, there is now evidence that they are
not a Triassic or Permian sediment but of much later date. This question of
the age of the deposits in this area will be returned to later. O~e result of
the numerous core samples obtained here has been to show that the Chalk
rests unconformably on the Jurassic in this mid-Channel area and this
suggests that the marked overlap seen in the Cotentin peninsula and in
the western outcrops in southern England is of importance here also.
The recent sampling with the " free-drop " corer in the western parts
of the Channel has confirmed and amplified the previous records and shows
that the site of the present Channel must have been a trough throughout
Mesozoic times, sometimes receiving much sediment and at other times
probably undergoing erosion.
This is no new conception, as reference to palaeogeographical maps will
show, but whereas many of these reconstructions were based on relatively
few and scattered dredgings or on the interpretation of the sources of the
heavy minerals in the various Mesozoic rocks of south-eastern England,
there is now a very fair " cover " of samples of" rock-in-place ". Further
work will undoubtedly improve the accuracy of the map and discover
outcrops of other formations, but I think it is unlikely that the general
picture wilt be shown to be seriously wrong.
What, then, is this picture, and what, with the aid of the geophysical
data, can we say regarding the history of the area ?
Let us take first the geology of the sea floor. One of the most striking
features of the floor of the English Channel is that the major part of it is
free from recent sedimentary cover, apart from a thin layer of large stones
and pebbles scattered about on the surface ; it is only in the larger embay-
ments like West Bay, off the Dorset coast, that recent muds have proved

80 w.B.R. KING ON THZ [vol. cx,
too thick to be penetrated by a 3-foot coring tube. In almost all other
areas failure to reach solid rock was due to the corer striking boulders
(usually flints).
When the results are plotted, the outstanding feature is the abundance
of records indicating the presence of " Chalk " as the outcropping rock.
It is clear that the Channel is the site of a tongue of Chalk running out
towards the Atlantic, but there are fairly frequent records of Tertiary
foraminiferal limestone overlying the Chalk. These show mainly as
pebbles and so may not indicate the exact position of the outcrops, but
being of not very hard limestone it is unlikely that they have travelled far.
Some cores clearly show Tertiary limestone in situ. Dangeard's work had
shown that there were deposits of Tertiary foraminiferal limestone over
quite large areas south-west of Jersey and Guernsey, between these islands
and the mainland of France. Probably these Tertiary deposits rest
directly on the older rocks of the Armorican massif, although the frequent
presence of flints on the French coast may indicate that some Chalk now
underlies the Tertiary or formerly existed in this embayment and was
weathered to a flint-bearing residue in pre-Tertiary times, and that this
residue, like that found on the granite of Flamanville, is the source of the
flints in the beach gravels.
A point of some interest in connexion with the Tertiary limestones of
the western Channel (including the Channel Islands area) is that all the
records are of cream or buff-coloured limestones crowded with miliolinid
forms (Quinqueloculina, etc.) and that few records of nummulitids have
been obtained, while in the eastern Channel such records as exist are of
nummulites and none are of miliolinids. Ia the Paris basin, however, beds
rich in both types of fossils occur, and it is felt that the difference is due
to facies and collection failure rather than to the existence of two separated
basins of deposition. Most palaeogeographical reconstructions of the
Eocene show the English Channel in existence, with the Paris basin re-
ceiving most of its fauna from the Aquitaine basin by way of the Channel.
Dangeard points out the numerous records of both miliolinids and num-
mulitids from limestones on both the southern and northern coasts of
Brittany and the records, whether from Dangeard, Crawshay, Worth,
Hunt or new ones, suggest that these Tertiary foraminiferal limestones
occur in small scattered outcrops over much of the area of the western
Channel; moreover, since no one of the outcrops appears to cover a large
area it is unlikely that the maximum thickness of these beds is anywhere
great. For the purpose of later reconstructions it is assumed that 100 to
300 feet is probably the right sort of figure for the thickness of the Tertiary
sediments in the western Channel. Here it may be noted that many
years ago Cole recorded the presence of Miliolina limestone well out in the
Atlantic at 51~189 12~ and at 51~ 11~ associated
with chalk and flints, and he suggests that this indicates that the Eocene
sea should be extended somewhat farther to the north than is shown by
de Lapparent and others. It will be seen later that this interpretation is
clearly in line with the views expressed in this Address.
The problem of the outcrops and thicknesses of the Tertiary of the
eastern parts of the Channel is rather different. We have the deep syn-
cline of the Hampshire basin with Tertiary sediments estimated at some
2000 feet, although the thicknesses of all the horizons are known to vary
markedly and rapidly. On the French coast there is little evidence of any
deep syncline, for although the steep anticline of the Pays de Bray is, in
general, to be equated with the anticline of the southern part of the Isle of

part 1] EN(~LISHCHAN~EL 81
Wight, the main syncline to the north of the Pays de Bray, that of the
Somme, shows none of the deep folding of the Hampshire basin. More-
over, the marked anticlinal structure of the Pays de Bray dies out both to
the east and west and is replaced by much less intense folding even before
the French coast is reached at Dieppe. The large area shown as Tertiary
on my 1948 map may therefore be due to quite gentle folding and may
contain sediments which are to be measured in a few hundreds of feet
rather than in the large figures of the Hampshire syncline. Future work
may easily prove it to consist of a number of smaller outcrops. In justifica-
tion of this estimate of thicknesses we have Dangeard's records of
nummulites from three stations in the eastern Channel and the presence
of numerous nummulites washed up on the beach near ]~taples on the
French coast. These suggest derivation from the Eocene (Bracklesham
Beds) or the lower part of the Calcaire Grossier of the Paris basin, and on
this slender evidence I have taken a figure of 700 feet in the synclines and
300 feet in the intervening anticlinal area as the maximum thickness of
the Tertiary beds in the eastern Channel. Further work will probably
necessitate considerable adjustment of this estimate.
Here we must return to the problem of the age of Dangeard's record of
" Trias " in mid-Channel between the Isle of Wight and Cherbourg, and
I have already mentioned that this may be a false identification. Along
an E.-W. line between l~ and 2~ a number of cores have been ob-
tained. They are samples of red and pale grey mottled clay, fine silts,
brown and grey soapy clay or dark loamy sands; both to the north and
south, Chalk has been proved by coring.
Professor F. W. Shotton, when looking at my specimens, was struck
by the similarity of the brown-grey soapy clay to a Tertiary pipe-clay and
this led to a re-examination of all the specimens in this 30-mile strip,
with the idea in mind of a Tertiary age for all the deposits in it.
A number of samples had already been washed for microfossils but
none had been found, and Mr. N. F. Hughes had examined a number of
the silts, also with negative results.
Amongst the cores obtained in this strip were five good ones of soft,
dark, sandy clay with shell chips. These had been thought to be of Recent
age but now the possibility of a Tertiary age had to be considered. I
therefore turned to Mr. D. Curry, whose knowledge of the Isle of Wight
Tertiary rocks is unsurpassed, to see whether he could recognize any
fragments of diagnostic significance.
His examination has produced results of the greatest value and I hope
they will be published in full in the near future. He has, however,
generously given me permission to use now the main conclusions to which
his study has led him.
Samples from five cores have been washed. Number 45, from 50~
1~ is a dark grey silty clay which has yielded small fragments of
a dark phosphatic shell probably referable to Lingula; lithology and this
fossil evidence mean that the rock is probably from the upper part of the
London Clay of the silty Hampshire type.
Two other cores, No. 49 (50~ 1~ and No. 60 (50~
1~ also appear to be of London Clay with characteristics similar to
No. 45. Number 60 is as nearly as possible on the site of Dangeard's
No. 395.
The two other cores, Nos. 51 and 52, from 50~189 1~ and
50~189 l~ have yielded a large number of fragments of macro-
fossils and numerous microfossils. Amongst the more important finds
Q.J.G.S. 1~o. 437 o

82 W.B.R. KING ON THE [VOI. CX,
are over a dozen specimens of Nummulites cf. variolarius, a long list of
ostracods and mollusca, including Ancilla cf. arenaria and Lutetia sp.
This fauna leads Mr. Curry to the conclusion that these beds must belong
to the Lower Tertiary, almost certainly to the Bracklesham Beds and with
a fair probability to an horizon near the level of Fisher's bed 21 of the
Bracklesham locality. Amongst the washings were a number of polyzoa,
which Mr. A. G. Davis has examined. These are all Eocene forms and
Mr. Davis independently suggested correlation with bed F21 of Brackle-
sham. There are, however, one or two forms very common in F21
which are missing in our samples, particularly Corbula pisum. It may
be that although the facies is similar to F21 the horizon is slightly different.
The fossil evidence is, however, conclusive that Eocene strata occur in
this strip of country, and since the rest of the " solid " rocks can all be
matched with other Lower Tertiary rocks of the Hampshire basin better
than with rocks of any other geological formation, I feel that there is
every reason to say that all the beds are of Lower Tertiary age and that
Dangeard's " Trias " is in fact also Tertiary. I have assumed a tentative
figure of 600 feet for the maximum thickness of the Tertiary beds in this
syncline.
Another point in favour of the Tertiary age of all these rocks is the
fact that one of the few highly fossiliferous chalk corcs with abundant
bryozoa and foraminifera has been identified by Mlle. Durand, of Professor
Milon's staff at Rennes University, as Senonian of a high zone--this chalk
was closely adjacent to one of the Tertiary cores.
Figure 1 shows the suggested extent and thickness of the various out-
crops of Tertiary rock in the Channel. The evidence for the boundary
of any of the outcrops is not very certain and the values for the thicknesses
are even less satisfactory. However, in order to build up a synthesis they
may be taken as a working hypothesis.
The Cretaceous beds may be considered in two main groups ; the Chalk
above, and all the rest of the Cretaceous strata, including the Wealden,
below.
In dealing with the Channel the Chalk must be considered as a unit.
Although most of the records indicate that it is " chalk with flints " that
is found, it is known that in many localities the Lower Chalk is as flint-
bearing as the Upper ; the presence of flint cannot therefore be taken as
diagnostic of age in this area. It is probable that detailed work on the
microfauna will enable many of the Chalk specimens to be dated, but the
fact that the surface of the Chalk under the sea tends to become lithified
makes study of the microfauna more difficult than usual.
The records of " chalk " in the eastern Channel are few and no recent
work has been undertaken there, but in the mid-Channel area (Isle of
Wight to Cherbourg) there is much evidence. Records taken in the area
some 10 to 20 miles south of St. Catherine's Point are numerous and enable
the boundaries to be drawn with considerable accuracy. It seems
reasonably certain that along the line I~ Chalk occurs continuously at
the surface to 50~
In mid-Channel, however, between l~ and 2~ a considerable area
has been proved where Jurassic and Wealden beds are exposed, indicating
an anticlinal uplift between two synclinals filled with Chalk. Before 3~
is reached, however, this anticline bringing up the Jurassic appears to
have died out, for a fairly continuous record of" chalk " has been obtained,
with one exception to be noted later. The northern margin is well
authenticated by finds of fossiliferous Upper Greensand at 50~

part 1] ENGLISH CHA~NEL 83
/~ /
/ /
//~ ~-x.
/" 8/
41. I I
I. 8
I
<D
~
n~
r
O
t~
I.

84 W.B. R~ KING ON THE [voh cx,
3~ Similarly, farther west to 4~ between 50~ and 49~
chalk is found at almost every station, even where there is evidence from
pebbles of Tertiary limestones.
Along 5~ and farther west most of the records are from Dangeard.
They are of " zoned flints " rather than actual chalk, but he gives strong
reasons for considering that they indicate Upper Cretaceous in situ. A
few corer samples were obtained by Dr. Hill around 49~176 and
4~176 all of which contained pebbles of chalk as well as flints,
but none of them could be claimed as absolute evidence of chalk in place.
In this connexion the records by Cole are of interest, for in all the dredgings
west of Ireland flints and even pebbles of chalk appear to be present, indicat-
ing that the site of the Atlantic to the west and south-west of Ireland was
covered by the Upper Cretaceous sea. Cole gives reasons why the samples
are of chalk in situ rather than glacially transported pebbles.
From all these records the outstanding conclusion is that most of the
Channel floor is formed of Chalk, in places overlain by Tertiary beds,
though in small areas the Chalk has been removed by erosion from anti-
clines to expose the Jurassic strata or the Lower Cretaceous beds.
Before trying to estimate the thickness of the Chalk in the various parts
of the Channel we must plot the known thickness as still preserved in the
two land areas.
In the Isle of Wight the Chalk is known to total some 1700 feet but west-
ward it thins rapidly, partly because it was originally thinner in the west
and partly because it is cut off by the basal Tertiary unconformity. In
Devonshire this thinning has reduced the figure to some 300 feet of Chalk
with about 70 feet of Upper Greensand, and much evidence has been
brought forward to show that these beds were laid down in a sea with its
coast-line abutting against the highlands of Dartmoor, so that parts of
the granite highlands were undergoing erosion throughout Chalk times.
East of the Isle of Wight, in Sussex, the thickness of the Chalk is less
than in the Isle, but 1000 feet is given as an average and even where the
Tertiary rocks overlie the Chalk considerable reduction of original thick-
ness took place by erosion before the first Tertiary beds were deposited.
The evidence regarding the present distribution and thicknesses of the
Chalk in western :France is similar to that for southern England. In the
centre of the Paris basin the Chalk is some 1800 feet thick but it is consider-
ably less thick in the marginal areas of Picardy and Artois, even where
patches of Tertiary rocks are preserved. The maximum in the coastal
areas seems to be nearer 700 or 800 feet. Thus the actual thickness still
present below 100 feet below sea-level (the plane of projection for the map)
is frequently not more than 300 to 500 feet, passing to a feather edge
south of Boulogne and north of Le Havre.
To the west, in the Cotentin peninsula, near Ste M~re ]~glise, thin
Cenomanian is overlain directly by thin Maestrichtian limestones, while at
Roscoff Chalk is banked against the cliffs of the Armorican massif. Thus
within the Chalk on the French side of the Channel non-sequences develop
towards the west, with consequent thinning due, as much as anything, to
lack of deposition. A little farther south the well-known Sables de Perche
indicate an approach to marginal conditions of sedimentation against the
eastern edge of the Armorican massif, of a somewhat different facies to
that found against the eastern end of the Devon-Cornwall area in Britain
or the north-western parts of Brittany in :France.
These records suggest that the existing Channel more or less coincides
with the original gulf in which a tongue of the Chalk sea was confined

between the remnants of the highlands of Devon and Cornwall to the
north and the Armorican uplands to the south. Perhaps these uplands
were largely swamped by the end of Cretaceous time. Whether and where
the relatively shallow Chalk seas opened to Cretaceous oceanic waters in
the west is a problem not connected with this study, but what does appear
is that in this western Channel trough the Chalk may contain a number of
intraformational non-sequences, and that it is nowhere more than a few
hundred feet in thickness. It is with these considerations in mind that
9the figures for the full remaining thickness of the Chalk have been put on
Fig. 2.
Turning now to the pre-Chalk Cretaceous rocks, the information is more
fragmentary, and variation in thickness is known to be extremely rapid.
In southern England thicknesses have been measured at outcrop and are
proved by a number of deep boreholes. Near Swanage 2700 feet is the
estimated thickness of Gault, Lower Greensand and Wealden, while in
West Dorset the two lower formations have pinched out and only 100 feet
can be found for the Gault ; and in Devon even this is generally cut out by
the base of the Upper Greensand.
In the Isle of Wight the thickness of these beds varies rapidly, with a
maximum of perhaps 2500 to 3000 feet; the Portsdown borehole shows
the definite figure of 1000 feet, while farther along the coast thicknesses of
this magnitude are to be expected in the southern part of the Weald and
under the South Downs.
Here note must be taken of the possible extension of the Paris Plage
ridge. The Henfield boring suggests that this feature may be influencing
Mesozoic deposition on an E.-W. axis stretching across the Channel into
southern England in the Beachy Head area. If this is so, the great thick-
nesses of the central Weald must be reduced in the actual coastal areas,
and therefore considerably smaller figures have been entered on the map in
the areas just south of the English coast. When we look at the pre-Chalk
Cretaceous and Jurassic rocks of the Boulonnais we see a state of affairs
quite unpredictable from a study of the English Weald only a few tens of
miles away. This should warn us against putting much faith in estimates
of outcrops and thicknesses in the Channel unless they have been checked
by samples or are supported by geophysical data. I realize that my own
lines will need altering as further evidence becomes available in the future.
In the Boulonnais the pre-Chalk Cretaceous and Jurassic rocks thin out
rapidly against the Palaeozoic substratum of Artois and even more
strikingly against the Paris Plage ridge, from both the north and the south.
Thin representatives of the pre-Chalk Cretaceous are found in boreholes
in the area of the Somme estuary, while farther south, in the Pays de Bray,
the Wealden and other pre-Chalk beds reappear, though in no great
strength (300 to 400 feet) ; north of Le Havre borings have proved some
250 feet of strata below the Chalk and above the Jurassic rocks.
From these extremely variable figures it is difficult to make any reason-
able estimates, but the fact that the Chalk appears to be cutting uncon-
formably across the Jurassic outcrops in mid-Channel, together with the
small values on the French coast, suggests that in the southern part of the
eastern and central Channel too large a figure should not be given to the
pre-Chalk Cretaceous and that towards the Brittany coast the pre-Chalk
Cretaceous is probably absent.
In mid-Channel, however, the Wealden has been proved in the central
area around 50~ I~
On the 1 : 1,000,000 French maps two records in mid-Channel between
Q.J.G.S. No. 437 G2

86 w . B . R . KING ON THE [VOI. CX,
_/
I
/
/ ]~
/
I '/
0 /
/
I" ~ o
x. /
~,.),L I:"" /
//
/
/
~~ ~ ~
@o
~
, . .~..9.~o. "~~.~--'~ . .~
/

I
~_.__J
/
C~
o
o
o"
~
"0
. l a
~
~
o~ ~.~
o

part 1] ~OLISH CHA~N~L 87
4~ and 5~ are marked as " Lower Cretaceous ". These are Nos. 527
and 534 of Dangeard's dredgings. They are quoted as being glauconitic
cherts and limestones and are entered by Dangeard as probably Ceno-
manian or Albian. Professor Milon has allowed me to examine No. 527
and it certainly appears to be of Upper Greensand facies rather than
" Lower " Cretaceous.
Another aspect of the problem has, however, been pointed out to me by
Professor P. Allen. On faunal evidence there is a strong presumption
that during Lower Greensand times the Iberian peninsula and southern
England were connected by a branch of the sea occupying the site of the
Channel, for the fauna of Punfield has affinities with that of the Iberian
area and is distinct from that found on the mainland of France at this
time.
Although the evidence for the thicknesses, or even the probable extent,
of the pre-Chalk Cretaceous strata is open to criticism, the map, Fig. 3,
may be taken as a working hypothesis of thesituation in this period of the
geological history of the area.
The Jurassic rocks are well exposed in both the English and French
coastal areas but not much was previously known of outcrops in the
Channel. Intensive coring in mid-Channel south of the Isle of Wight has
proved that here there is a large outcrop of Wealden and Jurassic strata.
South of the Wealden beds, Purbeck ostracod shales and Chara-bearing
cherts occur over a considerable outcrop before reaching typical fossili-
ferous Upper Kimeridge shales and clays. These have a general E.-W.
strike over a large area. To the west and south of this central Jurassic
outcrop are the well-known records of Lias both in the Hurd Deep and
south of the Eddystone. No new records have been obtained in this area
and there is no sure evidence of any Jurassic rock here other than Lias.
As might have been expected, Jurassic samples have been obtained south
of Portland, and one recorded 16 miles south of Start Point is probably a
Jurassic clay. These are of interest in fixing the northern limit of the
Chalk outcrop. There is no positive evidence that during the Middle and
Upper Jurassic times a gulf of the sea stretched westward along the site of
the Channel and on the map giving the thicknesses of the Jurassic nothing
has been added for the Middle and Upper Jurassic rocks. It is possible
that thin representatives were deposited and removed during the regression
of the seas in Wealden times or thin deposits may still remain under the
Cretaceous, but geophysical evidence, where we have it, seems to make
this unlikely. Along the English coast there are reasonably good records
of the thicknesses of the Jurassic rocks, both from outcrop measurements
and from boreholes.
The general easterly dip in Dorset necessitates a gradually increasing
figure from 300 feet near Lyme Regis (measured again at 100 feet below
sea-level) to some 4000 feet in the Isle of Purbeck. The Portsdown bore-
hole gave 4315 feet and to the east the values of 3946 feet at Henfield and
2760 feet at Grove Hill are well known.
The Grove Hill borehole suggests that the Paris Plage ridge was making
itself felt here throughout Jurassic time, while on the French side this
ridge caused the complete absence of Jurassic strata in its neighbourhood.
The Avennes and Ferri6res bores in the Pays de Bray give 4000 feet for
the complete Jurassic succession but this thins to 1287 feet near Le Havre
and 760 feet is recorded from the borehole at Dives; the full thickness
for the remaining Jurassic in the area is about 1000 feet. These figures
were in my mind when I constructed the Jurassic map (Fig. 4).

~8 W.B.R. KING ON THE [vol. cx,
j~ "... 9
.. 9 . .
.~
" -7-
/// oo
o 2~ ,
lp,/
,'..;.:..~...~/.~".'.~ .. :-..'."
9".~.~~,. ,,.:..,-
Z

0
A ~

,

~ --4..
I~-. I
I
, I
I ,/
2
.~ ~
r~
.~o
0
~,,,~

part l] ENGLISH CHA~NEL 89
f f ? ,
i l"-"// /~
// // )
0
~,.
/ / /
/ /
/ /
/ /
/ /
/ /
/ / / /
/ /
// / //
/~/ 9
/ / .: ,
~'-"--" / /. I
"--" / Ill_.__.ol
t "
i
I
f
I
I
I!

o I
9 I
Q,..~
o
~..)~
J-o ,.~
9,...i
~o

90 w.B.R. KING ON THE [VO1. CX,
The New Red Sandstone may be divided for the purpose of this study
into the Keuper Marl above and the sandstones, breccias and pebble-beds
beneath, the whole being spoken of here as the New Red Sandstone.
The Keuper Marl is found in its typical chocolate red-brown marl in
cores 12 miles south of the Eddystone, and judging by its position relative
to the Lias and Rhaetic (Worth's records) on the one hand and the New
Red Sandstone on the other, there can be no question that it is the Keuper.
At two localities in mid-Channel, north-west and north of Guernsey
(stations 64 and 2945), cores of chocolate red-brown marl have been
obtained. These have been washed and searched for microfossils but none
has been recovered.
The two samples differ somewhat in colour; No. 2945 is the slightly
maroon brown usually seen in the Keuper Marl while the other (No. 64) is
a brick-red and may be more easily matched by a brown specimen of
Weald Clay. There is ample evidence of chalk in situ in close proximity
to both occurrences, but since the Chalk is unconformable on the lower
beds the samples may indicate that here slight anticlinal uplift has brought
pre-Chalk rocks to the surface.
At station 2945 (49~ 2~189 however, pebbles of foramini-
feral Tertiary limestone were recovered from the thin gravel overlying the
clay. This might suggest a Tertiary age for the clay, but, on the other
hand, the site is not far from Hill's station 2 (50~ 3~189 which
recorded only 160 feet of low-velocity material above beds having the
velocity usually attributed in this area to the New Red Sandstone.
On balance I am inclined to consider, as a working hypothesis, that these
samples indicate eroded anticlinal areas where the Keuper Marl is peeping
through the cover of Chalk.
These stations lie between the known Lias of the Hurd Deep and the
New Red Sandstone south of Start Point and their records suggest that
beneath the Chalk (and some Lias and perhaps a little Lower Cretaceous)
the western Channel is over large areas occupied by Keuper Marl. Be-
tween the Keuper Marl-Lias records and the coast, New Red Sandstone
has been proved by numerous corings and the arrangement of the outcrops
has been described (Hill & King 1953). These show that the metamorphic
rocks of the Eddystone and Bolt-Start area are to be interpreted as the
tips of hills projecting through an infilling of New Red Sandstone and that
planed-off Devonian south of Plymouth is also covered by these red rocks.
Ordinary methods of geological investigation can give no information
about the New Red Sandstone in the mid-Channel area, for no outcrops
of that .formation, or of the underlying older rocks, occur until the Armori-
can massif is reached on the Brittany coast or in the Channel Islands.
The records so far obtained justify, I think, the map (P1. IV) of the
approximate outcrops of the solid rocks under the waters of the Channel.
(The boundaries on the land areas have been drawn, as in 1948, at 100 feet
below O.D. to eliminate the complications of topographical control on the
adjacent land areas.) To complete the picture, however, we still need
definite figures for the thickness of the :New Red Sandstone rocks.
In 1947 M. :N. Hill began his geophysical seismic refraction work, using
sono-radio buoys. His work, the results of which have been published in
various journals, has enlarged our understanding of the structure of the
western Channel to a degree which would otherwise have been impossible.
Our thanks should also here be recorded to those institutions which have
allowed us to do the geophysical and coring work from their vessels.
Particularly are we indebted to the Director of the Marine Biological

Association Laboratory at Plymouth and the captain and crew of the
SabeUa ; to the former for the facilities afforded and to the latter for their
skill in handling the apparatus and their good will, enthusiasm and interest
in the work. Our thanks are also due to the Director of the Institute of
Oceanography for the use of Discovery II during a week in June 1952.
During one of our trips in Sabella we had the use of the Decca Navigation
System, which was lent by the Company for the duration of the trip, the
cost of installation being paid for by a grant from the Scott Fund of the
Royal Society. The use of this navigation aid enabled the positions of the
coring stations to be fixed within a few yards, as compared with the very
approximate positions obtainable by dead reckoning, aided by sun sights
when that was possible. It may be noted that the important sites where
Tertiary beds have been found in the mid-central Channel are Decca fixed.
Seismic records taken along several lines in the western Channel have
enabled us to draw reasonably accurate sections down to the Armorican
basement; one line runs from Plymouth to near the French coast.
Working from the known geology in the coastal regions and the outcrops
given on the New Red Sandstone map (Fig. 5) it is possible to interpret
the geophysical data in geological terms.
The marked difference in velocities between the New Red Sandstone
and older rocks enables the position of the base of the New Red Sandstone
to be drawn with considerable accuracy. It will be noted that whereas
the northern margin of the New Red Sandstone deep trough lies not far
south of the Eddystone, there is fairly good evidence that the southern
edge of the trough is some 20 to 30 miles north of the Brittany coast.
The important figure, however, is the 3000 odd feet of New Red Sandstone
over much of this part of the western Channel.
At Hill's station 5 (20 miles north of the French coast) it was found
necessary to bracket the Lias, Chalk and Tertiary, and the figures indicate a
combined maximum of 1000 feet about 49~ 4~ This may include
some 300 feet or so of Tertiary deposits. To apportion the remainder
between the Cretaceous and the Jurassic we must consider the probable
conditions during Upper Cretaceous time. As already mentioned, there
is every reason to believe that there were non-sequences during this period
in the western and south-central Channel ; it is considered that there are
300 to 500 feet of Chalk where Tertiary rocks have been proved, but this
thickness will be reduced to a feather edge where Jurassic or Triassic rocks
outcrop.
In the foregoing pages reasons have been given for the estimated thick-
nesses of the post-Triassic rocks over the whole of the Channel, and
although the figures do not pretend to be accurate they are likely to be of
the right order. In general, they do not vary greatly from those given
by me in an unpublished lecture to the Challenger Society in 1949--figures
that were available to Browne and Cooper in their work on the gravity
values of the Channel area.
In so far as the New Red Sandstone thicknesses are concerned we have
the definite figures obtained by Hill in the western Channel, and a few
records of thicknesses, and localities where New Red Sandstone is known
to be absent, both in England and France. From these it is possible to
estimate the total thickness and distribution of the New Red Sandstone
in the central and eastern Channel. It is to be hoped that seismic work
will be carried out in mid-Channel in the central and eastern areas by which
to check these figures.
Most authors who have drawn palaeogeographical maps have con-

92 w.B.S. KING O~ THE [VO1. CX,
sidered that in the early part of the New Red Sandstone period the South
Devon-Channel area was a separate cuvette from that of the Midlands,
and that only in Keuper times were they joined. But, as Kent {1949)
has pointed out, this conception is based largely on the assumption that
the Mendip axis continues to the east, an interpretation he shows to be
now untenable.
It may well be, therefore, that the New Red Sandstone is at its thickest
in a zone which includes the Channel south of the Isle of Purbeck and the
Dorset-Hampshire area, and that there was a passage {perhaps quite
narrow) from this euvette via the Severn basin through which much of the
tourmalinized material and the few fossiliferous pebbles with Orthis
budleighensis reached the Midlands. That problem is, however, outside
the main scope of this study. It is from the borehole evidence in the
coastal land areas of England and France that reasonable assumptions
can be made of the probable occurrences of New Red Sandstone rocks in
the Channel and adjacent mainlands.
In south-eastern England there is the definite presence of the Keuper
at Portsdown and Kingsclere, and the absence of the Trias in the borings
to the east and north-east. This suggests that where we do find Trias, it
is infilling valleys that drained from the north-east or east towards the
main basin lying in the neighbourhood of Bournemouth.
In the coastal areas of North-West France there is fairly thick Trias
filling in a narrow tongue which runs from the neighbourhood of Falaise
north-westward past Bayeux and along the eastern side of the Cotentin
peninsula. The evidence appears to suggest that the main tongue of
Trias must lie to the east of the Cotentin peninsula and run in a north-
westerly direction towards mid-Channel. Trias is absent from borings at
Caen and Dives, at Commes and Merville on the coast thin Trias is found
and in the area of the Seine estuary it is again absent. Farther north
another tongue of Trias was proved in the Ferri~res boring in the Pays de
:Bray. No Trias was proved in a number of borings between the Somme
and the :Boulonnnais except at Merlimont, where 20 feet of doubtful
Trias was found. This all suggests that there are a number of narrow
troughs draining off the Palaeozoic areas of North-West France filled with
Triassic deposits which thicken as they converge on to the main cuvette
of the Channel area.
At a few exposures south of Aire and in the boring at Framzelle, near
Cap Gris-Nez, Triassic marls and pebble-beds are recorded. The direction
in which the valleys that contain these rocks drained is obscure but it may
have been down the centre of the Channel to join with those coming from
the east and south-east.
That much material was washed off the Armorican massif in Triassic
times has always been accepted, but in Brittany no trace of deposits of
Triassic age appears to have been preserved. In the Channel area near
the coast of West Dorset, Devon and Cornwall samples of New Red
Sandstone have been obtained frequently in the past and on many
occasions during the recent coring operations, while at 49~ 2~
and 49~ 3~ two good but puzzling cores were obtained; two
possible interpretations of them have been discussed on p. 90. Otherwise
there are no records in the Channel itself of what may be New Red Sand-
stone outcrops.
The boundary between Trias and Lias appears to run out from the
coast west of Lyme Regis, swinging away some 30 miles from Start Point
to an E.-W. line 20 miles south of the Eddystone. In places it is over-

lapped by the Chalk unconformity : for example, 12 miles due south of
the Eddystone.
The base of the New Red Sandstone is also well documented in this area
and clearly follows the present coast closely, as shown on Fig. 5.
Yet all these data enable us to draw only a very approximate and
diagrammatic map of the areas where New Red Sandstone still exists,
either forming the surface or at depth covered by newer rocks ; geological
evidence by itself is silent about the thickness of New Red Sandstone.
At this point Hill's geophysical work comes mightily to our aid. The
records of the long line of stations reaching southwards from Plymouth
almost to the French coast enable us to determine the thickness of the
New Red Sandstone deposits in this part of the Channel. As was shown
in our 1953 paper, the New Red Sandstone fills a 600-foot basin between
Plymouth and the metamorphic ridge of the Start-Bolt-Eddystone, and
these metamorphic rocks and the East and West Rutts are the tips of pre-
New Red Sandstone hills probably recently re-excavated from their cover
of red sands and-breccias. South of this ridge, however, the base of the
New Red Sandstone drops away to 3000 feet or more, then flattens out
for 65 miles before rising again fairly rapidly to be cut off by the base of
the Cretaceous 20 miles before the French coast is reached near Roscoff.
Further work in 1952 by Hill along two lines, one N.-S. about 3~
and the other NE.-SW. from 50~ 3~ to 49~ 4~ as
yet unpublished, indicates a similar situation. Dr. Hill and Mr. A. A. Day
have generously allowed me to incorporate in this Address advance infor-
mation of their results. From all the data thus available the reconstruc-
tion of the New Red Sandstone occurrences (Fig. 5) has been prepared.
The thicknesses in the central and eastern Channel are estimated but in
the western Channel the figures are probably not far from the truth;
these demand that we should expect at least 4000 feet of New Red Sand-
stone in the neighbourhood of the Isle of Purbeck, probably thinning
away into the various deep valleys whose ends are known on the land
areas.
Mr. N. L. Falcon and Mr. L. H. Tarrant have kindly discussed some of
the points raised here and have given me the data obtained from the
D'Arcy Exploration Company's seismic work near Wareham and Ports-
down. It appears that the actual depth to the Palaeozoic floor in the
Wareham district is difficult to deduce from the records but it certainly
is not less than 7500 feet nor more than 10,000 feet below sea-level,
probably near the greater depth. This would necessitate between 3500
and 4500 feet of New Red Sandstone in this locality, a figure agreeing well
with the estimates arrived at by the line of reasoning given in the preceding
pages. The figure of 8500 feet for the Palaeozoic floor at Portsdown
needs about 2000 feet of New Red Sandstone, which would indicate that
the thinning of that formation, from its maximum probably in the Bourne-
mouth area, is well under way at Portsdown and that the formation may
fail altogether some considerable distance west of Henfield, where we
know it to be absent.
Two of the valleys just mentioned must run from the deep basin south-
east to Normandy, another towards the Pays de Bray and perhaps another
up Channel. There is very little evidence, however, to show whether the
Trias of the Boulogne area should be joined by a valley running down the
central Channel or whether the valley might follow a line north of the Paris
Plage ridge to the neighbourhood of Portsdown. This latter line would
appear on general grounds to be more probable but there is no confirmatory

94 w.B. It. KIN~ O1~ THE [vol. cx,
I
I
/ /
1"7/ /
/ /
/ /
/ /
/
/
f~, I I
/ ,..~,~.
I i,I i--,~./
x/zz-._, q

i
"~1 /
, )
I//I i~
I I I
I I I
Q ~
II
r
~
0
r
0
. ,,,,j
~
S ~.~~
~) "~ 0
!~176
o ~
~ .i~
~.~
~.~

borehole evidence along the south coast of England and such bores as
have passed through the Jurassic rocks have not found the Trias beneath.
On the map I have shown three arms running towards the east and south-
east but I have not dared to prolong one to the Boulogne area.
If we assume, as a working hypothesis, the thicknesses marked on the
maps (Figs. 1-5) we can rough out the shape of the sub-New Red Sand-
stone floor, usually spoken of as the " Palaeozoic floor "
In the resulting map (Fig. 6) contours have been drawn at 2000-feet
intervals; no allowance has been made for faulting, which in some areas
may be of considerable importance.
The map produced by Kent (1949) from a careful study of all the data
from the English mainland and the French coastal area north of the Pays
de Bray agrees well with the lines for the Channel on my map.
Hill's work in the western Channel gives much definite information, and
north-west of the Channel Islands, at his station 2, there seems to be very
clear evidence that the Palaeozoic floor must lie about 2000 feet down.
In the interpretation adopted here this station marks the southern margin
of the deep trough rather than lying over its northern slope.
The great basin which includes the Isle of Purbeck, the Isle of Wight,
the mid-central and mid-eastern Channel and the Pays de Bray in France,
is of composite origin. In the west its depth is due to great thicknesses of
New Red Sandstone, together with maximum Jurassic deposits, but it
contains no Cretaceous or Tertiary rocks. The same may be said of the
central mid-Channel area. In the Hampshire basin the New Red Sand-
stone is considered to be thinning to the east, but the addition of the thick
Cretaceous and maximum Tertiary rocks puts the Palaeozoic floor here
at about 13,800 feet below the surface.
In the mid-eastern Channel the New Red rocks probably thin markedly
towards the east but the Jurassic rocks must maintain their full thickness ;
the Chalk gradually thins eastward, as does also the pre-Chalk Cretaceous.
The result is that the contours close towards the east but may open again
south-east of the Pays de Bray to show greater depths in the centre of the
Paris basin.
In 1951 Mr. R. C. S. Waiters delivered an address on " The Rocks
between France and England " to the British Section of the Society of
Civil Engineers of France in which he showed a map of the contours of the
Palaeozoic floor. Since then much new information has become available
and his map needs modification.
In the paper by Browne & Cooper (1952) on " Gravity measurements in
the English Channel " the authors used, besides published figures, the
estimates of the thickness of the cover rocks above the Palaeozoic floor
which I then considered most probable (table 4, p. 438). It is unlikely
that the figures now given would affect their results to any appreciable
extent, for they state (p. 435), " It is for the present purposes immaterial
whether the geological model used is accurate in its details." On looking
at their map 7 (p. 445), it is clear that after making corrections they are
left with two main areas of anomalies--a large area of negative anomalies
north-east of Barfleur and a large area of positive anomalies in mid-
Channel south of Plymouth.
From Hill's work we know that the positive values south of Plymouth
cannot be due to anything above the Palaeozoic floor, and whatever the
cause of the positive anomalies may eventually prove to be they suggest
that there are no large granite intrusions in the Palaeozoic in this area, for
these would produce negative anomalies. On the other hand, I personally

96 w.B. It. KING ON THE [vol. cx,
f
I
J
J
q,ooO"'i I /"
o~ //
/~o~ /
,I I I1,: oo
fo/,,l~~o# I
}o/,,Ol,/
I / I
~ l l III d
F I I/I, ,/
,~ ~ I" 11'71 ~'---1--~-.~
--,._ [ ./
-~,8 / I "

_
I
o
--..~
/
/
I
I
J
/
/
/
/ i
I.
0
8_a_
~.f~
~.o
a_-~
..0
o.,,.i
o
o
-8
o
r
o
o~D
0
0
l

part 1] ENGLISH CHA_WNRL 97
think that the negative values north-east of Barfleur indicate the presence
of large granite intrusions in the Palaeozoic rather than a great thickness
of Coal Measures (Browne & Cooper 1952, p. 446). The presence of basins
filled with Coal Measures is reasonable on general geological grounds in
the areas where this is suggested by Falcon & Tarrant (1951), but it is
unlikely that thick Coal Measures would occur in the regions of low
gravity north-east of Barfleur, where granite is known to be present.
The evidence brought forward in the foregoing pages leads to a fairly
clear picture of the history of the Channel since the end of the main
Armorican mountain-building movements when the erosion effects acting
on the newly formed mountains had had time to establish a definite topo-
graphy.
Violent erosion of the Brittany mountains was sweeping coarse material
towards the north-central Channel area. Much material seems to have
moved down a wide open trough or valley from the west, but we have
little evidence as to how far west this trough stretched. New seismic
work may give us the answer. Bullard's early work suggested that it did
not stretch far, but he had only one line of stations and this may easily
not have crossed the trough.
The trough filled up with the breccias and sandstones of the New Red
Sandstone and finally with Keuper Marl. The great thickness of the
deposits may well indicate that the trough, as in later times, subsided
periodically, allowing more and more sediment to accumulate, rather than
that it was originally a very deep valley waiting to be filled. The sedi-
ments accumulated there because of the tendency of the area to subside,
a feature which has persisted up to the present time.
In the east, similar but narrower valleys or troughs brought material
from the east and south-east. Their sediments can still be studied from
Falaise to the Cotentin peninsula.
Within reasonable bounds, the limits of the New Red Sandstone in the
Channel and coastal areas of France and England are known. Do they
mark the original extent of the deposits or are these mere residual rem-
nants ? This problem has wide implications and leads to the question
whether some of the high summit-levels in western England are relics of
the sub-Triassic surface stripped of their thin cover, or even are the sub-
aerial erosion surface of Triassic times.
In the western Channel there is the trough, flat-floored and filled with
some 3000 feet of deposits. Its margins to north and south rise sharply;
in the south it is cut off by the Chalk but in the north, after rising from
3000 feet to the line of the Eddystone, it sinks again to fill a 600-foot basin
between the Eddystone and Plymouth. Here the New Red Sandstone
clearly is filling hollows and overtopping ridges, to bank up finally against
a cliff of older rocks. While this filling up of marginal basins was taking
place on the flanks of the uplands, presumably rapid erosion was still
proceeding on those uplands and one would expect the three-fold division
of desert topography to be present--the depositional basin, the pediment
and the residual uplands. By the time of the Keuper Marl, when the
deposit was mainly dust, the residual uplands would have been largely
worn down and what remained would be basin and pediment. The pedi-
ment in all probability was covered by thin sediments but these would
naturally have thickened with approach to the basins, which from all
considerations must have been sinking during their infilling.
In this way gently Sloping surfaces of the hard Palaeozoic rocks in
Brittany and Devon and Cornwall would have been formed which would,

98 w.B.R. KING ON THE [VO]. CX,
by the end of the Trias, have been buried under relatively soft sediments--
thick in what are now the basins, thin on what are now the uplands.
If it is correct to envisage the basins as areas of periodic subsidence
throughout Mesozoic and Tertiary times, it is reasonable to consider the
adjacent areas as suffering periodic upwarping. If this were so, then the
difference of elevation between the surface of the Trias-Rhaetic boundary,
for instance, in the marginal areas and the then surface at the centre of the
present uplands need not have been nearly so great as it now is.
Thus it should be no surprise to find that erosion in Triassic times had
not reached to the surface of the main Dartmoor granite; but this does
not carry with it the corollary that the present uplands were necessarily
standing high above their margins at that date. If the present uplands
were low-lying and covered by Keuper and Liassic deposits, this would
easily explain the absence of Dartmoor detritals in the Jurassic strata of
southern England.
As the periodic uplifts of the lands bordering the depressions took place,
much, if not all, of the soft sediments laid down previously would be re-
moved rapidly by sub-aerial denudation, and when a marine transgression
began it would therefore find a gently sloping surface of hard rock upon
which the waves could trim up the sub-Triassic pediment and convey the
impression that much of the denudation had been marine. It is not to be
supposed that in a great transgression the wave-cut surface would be
horizontal; it is more likely to have been sloping, with perhaps a cliff
development marking its final extent.
This conception of the filling of the central Channel with New Red
Sandstone and finally Keuper Marl, while the present uplands both on the
north and south were being planed off to a sloping pediment, suggests
that some of the high-level surfaces recently attributed to later Tertiary
erosion may be primarily of very much older origin. This, of course, is
no new idea but appears to be out of favour in certain quarters.
A further point is that if the marginal basins, now under the Channel
or forming the lowlands like the Cheshire and Worcester basins, are in
fact very ancient morphological features, then it is not unreasonable to
consider that much of the general coast-line of western Britain is con-
trolled by the positions of the margins of other Trias-filled basins. This
point has already been touched upon by Professor O. T. Jones in his
Address delivered three years ago. If this is indeed the case, as I believe
it is, then it may help in arriving at the history of Mesozoic deposition to
the west of the present outcrops. In the Channel there is plenty of evi-
dence that the Liassic sea invaded the area along the line of the Triassic
basin, and it has usually been assumed that a similar spread from the
Midlands across the Cheshire plain was the only path by which the Liassic
sea reached Antrim and the Western Isles of Scotland. May not, however,
Wales, Devon and Cornwall and also Brittany, and even Ireland, at this
time have been islands, with perhaps a narrow trough running along the
site of the Bristol Channel and also a main channel passing round the
Scilly Isles and thence northward through the St. George's Channel into
the main Irish Sea area, there joining the branch from the Cheshire basin?
Since there is no evidence of Middle or Upper Jurassic strata in the
western Channel there is no justification for supposing that the Oolite seas
necessarily followed a similar course, though there is nothing against it.
A boulder of calcareous sandstone was dredged up by the Marine Biological
Association ship due south of the Lizard at 49~189 5~ on 11
July, 1949. This boulder, some 289 inches in diameter, has yielded a

number of fossils ; these are not highly diagnostic but contain a number of
small Pectens, an oyster and a Pseudomontis. Dr. W. J. Arkell has kindly
examined these and considers that they most nearly match forms from the
calcareous grits of the Corallian or Kellaways Rock, but of facies more
like the West Scottish rocks than those of the English outcrops. If this
be so, we may have here a pebble which has been brought south by ice
and floating bergs rather than one obtained more or less in situ. Pebbles
or boulders are ahvays subject to this uncertainty, unless there are a large
number of the same type within a small area. Little weight can be put on
the occurrence of this single specimen until others are obtained.
During the Wealden, again, there may have been a branch of the
Wealden lake along the line of the Channel, but since this was a time of
general uplift the most that should be suggested is that this line was
probably the site of one of the rivers feeding the lake from the west.
How far west the Cretaceous transgression reached in Lower Cretaceous
times along the mid-Channel line is also unproved.
The two records on the French 1 : 1,000,000 map, between 4~ and
5~ marked as Lower Cretaceous, have already been noted and it was
pointed out that they should probably be referred to the Upper Greensand,
which is here included with the Upper Cretaceous, although the distribu-
tion of Lower Cretaceous faunas (as mentioned earlier) is in favour of a
marine trough along the site of the Channel at this period.
We have clear evidence that during the Upper Cretaceous the Chalk
spread far to the west along the whole width of the Channel trough,
although it was limited on the north and south by the Palaeozoic outcrops
which in early Chalk times were not far from the present coast-lines.
It is difficult to know how much should be allowed for post-Cretaceous
warping--clearly if there had been none in the western Channel and the
shore of the Chalk sea was well up on Dartmoor then the Chalk in mid-
Channel would have been extremely thick ; there is definite evidence that
this was not so. It is more reasonable to assume that the old basin or
trough of sedimentation subsided again in post-Cretaceous times. In
the central and eastern Channel there is clear evidence of post-Cretaceous
folding, but one of the chief difficulties in the interpretation is to know
how much of such folding there was in the western Channel. Professor
O. T. Jones, dealing with the Bristol Channel area, brought forward
evidence for continuing the Tertiary fold axes there to the west.
It is reasonable to assume that the Chalk seas spread across the troughs
and basins where the Trias had been deposited and, according to many
interpretations, actually spread over and covered the worn-down Triassic
pediments. If this was so, then in order to get the Chalk into the North
Irish Sea as well as into the western Channel there must have been post-
Cretaceous subsidence in the western basins whilst the whole of Britain
was receiving the gentle but persistent tilt down to the east which has
allowed the Midland Jurassic dip and scarp topography to develop and
has carried the East Anglian Chalk base down 1000 feet below sea-level on
the coast.
Nevertheless this does not militate against the thesis that the seas and
plains of western Britain are essentially Triassic basins which have suffered
downwarping at a number of geological periods and that many of the
" surfaces " now found on the upland areas, particularly those of the
Lower Palaeozoic of the west, are in their origin re-excavated Triassic
pediment surfaces uplifted at various times and tilted or warped in Miocene
and even early Plioeene times.

100 w.B.R. KING ON THE [vol. CX,
It remains now only to mention the Tertiary deposits. The great
thickness in the Isle of Wight owes its preservation to the deep syncline
which developed in post-Oligocene times; it must be assumed that sedi-
mentation of this extent originally spread over a much greater area and
that in most places it has been removed by erosion.
The areas covered by the early Tertiary seas in Britain and France are
fairly well defined and Dangeard's work in the Channel and the recent
coring have confirmed the presence of Tertiary foraminiferal limestones
over wide areas, with a considerable outcrop in mid-central Channel.
Again, we have the evidence that the Tertiary seas spread along the site
of the old Triassic trough, indicating a continued downwarp along the
same lines.
To what extent the Miocene movements affected the Channel area is
not easy to say. The violent folding of the Isle of Purbeck and Isle of
Wight and in the Pays de Bray would suggest that similar violent folding
might be expected in the eastern and central Channel. Work so far done,
however, suggests folding on a much gentler scale, with broad open folds
and quite gentle dips similar to those found in most outcrops of the Chalk
in England and France. Although faulting is probably present it has so
far been impossible to prove it. In the western Channel the great spread
of Chalk, with the scattered patches of Lower Tertiary and rare exposures
of pre-Chalk rocks, again suggests that no strong folds of Miocene age
occurred in this sector.
One or two points stand out clearly from the foregoing account. The
most obvious is that since the end of the Armorican mountain-building
movements the English Channel has in general been low-lying ; sometimes
an area of deposition and at others undergoing erosion, while the marginal
lands tended to undergo periodic upwarp. When marine transgressions
took place it was along the site of the Channel that arms of the seas
stretched far to the west. Whether waters also from a proto-Atlantic
stretched eastward up the Channel to join them is not clear, although
there are definite indications that at times this was so.
If the upland areas of western Britain were covered by the sea during
the main transgressions they must at those times have been low-lying
compared with their present elevation, for if this were not so, the deposits
laid down in the western Channel would not be of the relatively thin and
shallow-water character which actually we find.
There also does appear to be some justification for the suggestion that
much of the present upland areas of the west of Britain, perhaps also the
whole of Ireland, was blocked out before the end of the Trias and is now
merely showing a redeveloped and uplifted topography. This indicates
that palaeogeographical reconstructions of the Mesozoic should show a series
of islands, more or less of the size of the present British Palaeozoic uplands,
rather than the large land area usually depicted and called the southern
part of the North Atlantic continent. The present high-standing position
of these Palaeozoic uplands and the presence of lowlands or shallow seas
between them would appear to be due to differential movements of
Tertiary date which have re-emphasized, in broad outline, the plan blocked
out at the end of the Armorican orogeny.
LIST OF I<~EFERENCES
ARKEL~,W.J. 1933. The Jurassic System in Great Britain. Oxford.
B~OW~E, B. C., & R. I. B. COOPER: 1952. Gravity measurement~ in the English
Channel. Prec. Roy. Soc. B 139, 426-47.

Co~, G. A. J., & T. CROO~r. 1910. On rock specimens dredged from the floor of the
Atlantic off the coast of Ireland. Mere. Geol. Surv. Ireland.
CRAWSHAY, L.R. 1908. On rock remains in the bed of the English Channel. An
account of the dredgings carried out by SS. Oithona in 1906. Journ. Marine
Biol. Assoc. (N.S.) 8, 99-117.
DANGEA~D, L. 1929. Observations de g4ologie sous-marine et d'oc6anographie
relatives a la Manche. Ann. Inst. Ocdanographique, (N.S.) 6 (1).
1951. G4ologie regionale de la France. VII, La Normandie. Paris.
FALCON, N. L., • L. H. TARRANT. 1951. The gravitational and magnetic explora-
tion of parts of the Mesozoic-covered areas of south-central England.
Q.J.G.S. 1{)6[for 1950], 141-67.
HILL, M. N., & W. B. R. KING. 1953. Seismic prospecting in the English Channel
and its geological interpretation. Q.J.G.S. 1{}9, 1-18.
HUNT, A.R. 1889. Notes on the submarine geology of the English Channel off the
coast of South Devon. Trans. Devon Assoc. 21, 460-87.
JONES, O.T. 1931. Some episodes in tim geological history of the Bristol Channel
region. Rep. Brit. Assoc. 1930, Bristol, 57-82.
1952. The drainage systems of Wales and the adjacent regions. Q.J.G.S.
107 [for 1951], 201-25.
KENT, P.E. 1949. A structure contour map of the surface of the buried pre-
Permian rocks of England and Wales. Prec. Geol. Assoc. 60, 87-103.
KING. W. B. R, 1949. The geology of the eastern part of the English Channel.
Q.J.G.S. 104 [for 1948], 327-37.
1949. Geological problems of the English Channel. Challenger See. Ab-
stracts, 3 (1) 21-2.
LEES, G. M., & P. W. Cox. 1937. The geological basis of the present search for oil
in Great Britain by the d'Arcy Exploration Company Ltd. Q.J.G.S. 93,
156-88.
& A. H. TAITT. 1946. The geological results of the search for oilfields in Great
Britain. Q.J.G.S. 101 [for 1945], 255-313.
LEMOINE, P., R. ttUMERY & R. SOYER. 1939. Les forages profonds du Bassin de
Paris. M4m. Mus. Hist. nat. Paris, N.S. 11.
PRUVOST, P. 1930. S4dimentation et subsidence. Soc. Ggol. France, Livre Jubi-
laire, 2, 545-64.
WALTERS, R. C.S. 1951. The rocks between France and Britain. [Presidential
Address.] Soc. Ingdnieurs civils de France (British Section), 15 pp.
London.
WILLS, L.J. 1951. A palaeogeographical atlas of the British Isles and adjacent
parts of Europe. London.
WORTH, R.H. 1908. The dredgings of the Marine Biological Association (1895-
1906) as a contribution to the knowledge of the geology of the English
Channel. Journ. Marine Biol. Assoc. 8, 118-88.
EXPLANATION OF PLATE IV
Map of the approximate outcrops of solidrocks on the floor of the English Channel.
Scale : 1 inch to 27 miles approx.

6 °
-t-
• j 1
.+.
.s,.,
-!-
+ +
4-
• • • • • • • •
. . ~ . : ..,
• • • • • ~
4 °
"i'n• • _ •
::
.]_ -t.- .,,_ •
~S-+....
~ "..)7• • • • • • •• •
2 ° 0 o
Q.J.G.S. VOL. CX, PL. IV.
2 °
.:.: :..'.:..:.:.
O
O
oO O
O OOO
0
0 0
_ ^_0_ 0 0
~~i:: ~-~oOo~_-- =
:.:.'.'...-:.:: :'. : ....f..-.:
.......-":'..'""'::"" .... :...-~..
.. .:.-: :/f.;.:.: . ..
•.-- -.....) (
:,.';." :.,.
[,
• . .
.° .,
°'.
+
-4.-
-,!--
+
+
-I'-
::!.::i{:!b.:
• .. • , -, ,..
4- t + -t- -+
-..-.--..+ + 7
÷~, + ~- + . . . . . . . /
~ -I- " i-t- .4- -!~
• • 4- + . . . ... .... _ , . , . _ _ _ .
::.:?..:.....: i:.f.'.: +::.:-- + -=
o:-:.-i:. + + + ÷
~++++-+~"+~++ ::::.::,+++ + 7 ~ ~ ~ ~ + + ~=+~_~-+ -
+
/
I I
0 o oo.,I
O O OO"]
O O Oo~
TERTIARY
E"?CHALK • • • •
CRETACEOUS
SCALE IN MILES
5 O IO 20 30
I I I I I
MAP SHOWING THE APPROXIMATE OUTCROPS OF THE SOLID ROCKS ON THE FLOOR OF THE ENGLISH CHANNEL.
.TO °
,EJRASSIC
NEW RED SANDSTONE
OLDER ROCKS
40 5o
I I

Geological History of the English Channel

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Geological History of the English Channel

Similar to Geological History of the English Channel (20)

Recently uploaded

Recently uploaded (20)

Geological History of the English Channel