Gideon Algernon Mantell.

Geological excursions round the Isle of Wight, and along the adjacent coast of Dorsetshire; illustrative of the most interesting geological phenomena, and organic remains online

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Online LibraryGideon Algernon MantellGeological excursions round the Isle of Wight, and along the adjacent coast of Dorsetshire; illustrative of the most interesting geological phenomena, and organic remains → online text (page 10 of 21)
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in the strata which clearly belong to a very dif-
ferent epoch ; to a period geologically recent,
when the now upper surface of the chalk
was rent by earthquakes, and the mountain


masses of the cretaceous system acquired their
present position and configuration. For these
fissures are invariably connected with the surface,
and are more or less filled with clay, sand, gravel,
and waterworn flints, from the alluvial debris that
forms the subsoil of the country. These appear-
ances may be observed in the chalk underlying
the bed of gravel and clay, on which the Albion
Hotel at Freshwater-gate is situated.

Shattered flints. — Upon carefully extracting
a flint nodule from this cliff, it retains its original
form ; but upon examination it will be found
" shattered in every direction and broken into
pieces, varying in size from three inches in
diameter down to the minutest fragment, and
even into an impalpable powder. The flints thus
shivered, as if by a blow of inconceivable force,
retain their form and position in the bed. The
chalk closely invests them on every side, and till
removed, nothing different from other flints can
be perceived, excepting fine lines indicating the
fracture, as in broken glass ; but when moved,
'In \ fall at once to pieces. The fragments are as
sharp as possible, and quite irregular, being cer-
tainly not the effect of any peculiar crystallization
or internal arrangement of the material, but solely
attributable to external violence." Such is the


description of this remarkable phenomenon given
by Sir H. Englefield thirty years since.* The tabu-
lar and plated flint in the fissures is also shattered
in a similar manner. The nodules in the regular
layers are invariably in this state, in every locality
of the vertical and highly inclined chalk ; but the
separate nodules in the middle of the strata are
entire ; and in the horizontal beds, as for ex-
ample, on St. Catherine's, Boniface, and Shanklin
Downs, all the flints are unbroken. This shattered
condition of the flints has doubtless arisen, as
Sir Henry Englefield suggested, from the con-
cussion caused by the upheaval and disruption
of the once horizontal cretaceous deposits. The
disturbing force, though in many instances pro-
ducing flexures in the strata, was clearly exerted
violently and suddenly, and in such manner as to
shatter the flints without dislodging them from the
chalk. From the insulated nodules being generally
entire, it would seem that the greatest violence

* Sir H. Englefield's "Isle of Wight," pp.20, 21. The following places are
enumerated as exhibiting this phenomenon very distinctly : — Alum Bay — Pit
south of Carisbrook Castle, and near Carisbrook town — Arreton-pit — Brading-
Down-pit — BradingShute — Culver Cliff. Shattered flints are occasionally met
with in some parts of the Sussex and Surrey chalk. My attention was first
directed to the subject in 1S20, by a paper of Sir H. Englefield in the
•' Linnean Transactions;" and a chalk-pit on the top of North-street,
Brighton, now filled up, and the area built over, presented a fine example, for
every flint, though retaining its form, was reduced to fragments. See the
" Fossils of the South Downs," p. 152.



of the shock was exerted in the direction of the
lines of stratification.

Mr. Webster, in describing the shivered Hints in
the chalk at Handfast-point, on the Dorsetshire
coast, remarks that the nodules are not only much
shattered, bu1 appear as if they had been re-
duced to atoms while the rock was yet in a soft
state, for the fragments are in general separated
from each other, with chalk between them ; and
the broken pieces of flint are at such distances,
that it is impossible to conceive by what means
they could have been so far separated, had the
chalk been solid at the moment of their fracture.
The bent condition of the strata at Handfast-point,
which will be described in a future page, attests
the plastic state of the chalk at the period when
its upheaval took place.

The Chalk downs. — We now leave the sea-
shore to ascend the hill, and proceed along- the foot
of Alton Down to Compton Bay, which is about
a mile distant. The western part of the central
range of downs extends from the Needles Cliff to
Motteston Down, which is 700 feet high, and
is a narrow ridge nine miles in length, with
steep declivities on each side; that on the north
arises from the highly-inclined dip of the strata;
thai on ih. south is produced by the precipitous


escarpment formed by the sudden termination of
the cretaceous beds where they rise to the sur-
face. The summits of this range command views
of great extent and picturesque beauty, for both
the northern and southern shores are distinctly
visible.* From the Needles Down, may be seen
on the north Tollands, Colwell, and Yarmouth
Bays ; and on the south, Freshwater and Compton
Bays, and the di tant line of coast. The eastern
portion of this chalk range, from Arreton Down
to Culver Cliff, a distance of seven miles, is of
the same character, f

* A graphic description of the scenery from this range of hills is given by
Sir H. Englefield, chap. iii. The view from Buccomb Down, looking over
Carisbrook Castle and Newport in the vale beneath, is very splendid ; that
from Arreton Down is equally fine.

t The view from Ashey sea-mark, which is situated on this part of the
chalk-hills between Arreton and Brading Down, is thus described by the
Rev. Legh Richmond : —

"Southward the view is terminated by a long range of hills (Shanklin,
Wroxall, and,) at about six miles distant. They meet to the
westward another chain of hills, of which the one whereon I sit forms a
link, and the whole together nearly encompass a rich and fruitful valley,
filled with corn-fields and pastures. Through this vale winds a small stream
for many miles ; here and there lesser eminences arise in the valley, some
covered with wood, others with corn or grass, and a few with heath or fern.
One of these hills is distinguished by a church (New church) at the top,
presenting a striking feature in the landscape. Villages, churches, country
seats, farm-houses, and cottages, are scattered over part of the southern
valley. In this direction also appears an ancient mansion (Knighton),
embellished with woods, groves, and gardens. South-eastward is a broad
expanse of ocean, bounded only by the horizon. More to the east, in con-
tinuation of the chain of hills on which I am sitting (Ashey) rise two downs
(Brading and Yaverland hills), one beyond the other; both are covered with
sheep, and the sea is just visible over the furthest hill, as a terminating
boundary. In this point are seen ships, some of which are sailing, and

M 2


Ascending Afton Down, the summit of which
is crowned Avith a group of tumuli, the views
along the southern coast are lovely in the extreme.
When almost half way up the acclivity, the land-
scape to the west displays a magnificent coup
d'ce'd of the romantic scenery of Freshwater and
Scratchell's Bays, and The Needles ; and that to
the east affords a view of Compton Bay, Brook
Bay, and the coast, till it is lost in the remote

Cause of the configuration of chalk downs.
— From what has been stated as to the compo-
sition of the white chalk, and the formation of the
strata, the cause of the external configuration of
the verdant downs we are now traversing appears
sufficiently obvious. If we examine the spots
where the turf has been removed by the flint-
diggers, we perceive immediately beneath the

others lying at anchor. On the north the sea appears like a noble river (the
Solent), varying from three to seven miles in breadth, between the banks of
the opposite coast and those of the island. Immediately underneath me is a
fine woody district, diversified by many pleasing objects. Distant towns
Portsmouth and Gosport) are visible on the opposite coast; and numbers of
ships occupy the sheltered station which this northern channel affords them.
Westward, the hills follow each other, forming several intermediate and
partial valleys, in undulations like the waves of the sea, and bending to the
south, complete the boundary of the larger valley I have described, to the
southward of the hill on which 1 sit. One hill alone (St. Catherine's), the
highest in elevation, and about ten miles to the south-westward, is enveloped
in a cloud, which just permits a dim and hazy sight of a signal-post, a light
ind an ancient chantry, on its summit." — Annals of the Poor, lnj tin-
tut* Rev. Legh Richmond.


vegetable mould a thick layer of loose nodules
but slightly abraded, and in no instance worn into
the state of boulders, pebbles, or gravel. The
surface of the chalk covered by the flints is fur-
rowed and waterworn, like that of the exposed
chalk along the coast. From the state of the
loose flints, it is evident, that although they must
have been washed out of pre-existing strata,
they have not been subjected to the action of
the waves for any considerable period, like the
materials of the existing sea-beach. For when
masses of the chalk cliffs fall within reach of the
billows, the exposed portions of the flints are com-
pletely rounded before the nodules are loosened
and detached from the parent rock ; and so soon
as the flints are liberated by the wearing away of
the surrounding chalk, they are quickly driven
against each other and broken, and the fragments
ground into pebbles, gravel, &c. ; in this man-
ner are formed the shingle and sands that accumu-
late along the sea-shore.

From the state of the down-flints, it is there-
fore obvious that the deposits whence they were
derived, must have been less consolidated than the
present chalk, and have admitted of the removal
of the calcareous materials, and the consequent
extrication of the siliceous nodules from the rock,


in a comparatively short space of time ; and the
disengaged flints, after a very brief exposure to
attrition, must have been transported beyond the
reach of the waves.

From the organic composition of the chalk
{ante, p. 1 80), it is manifest that when first deposited
at the bottom of the ocean, it was a fine white
detritus or mud, resembling in its nature and ap-
pearance the chalk now in progress of formation,
along the coasts of the Bermuda Islands ;* some
layers of which are as rich in microscopic shells
as any of the cretaceous strata. The veins and
beds of flint, as we have previously explained,
probably originated from the periodical introduc-
tion of thermal waters highly charged with silica,
into the calcareous sediment. The subsequent
conversion of the incoherent detritus into compact
limestone, may have resulted in part from pressure,
but principally from the slow infiltration of crys-
talline carbonate of lime ; a process which has so
rapidly converted the mud of the Bermudas into
a rock fit for building, that the imbedded shells
in many instances retain their natural colour and

It may therefore with great probability be as-
sumed, that at the period when the cretaceous
■ Wonders of Geology, vol, i. p. (>9.


strata were subjected to those elevatory move-
ments which ultimately raised enormous moun-
tain-masses of chalk, together with the wealden
deposits on which they rest, above the level of the
sea, the last formed, uppermost, and of course
least coherent beds, would be the first exposed to
the action of the waves ; and if the elevation were
gradual,* successive layers would be subjected to
the same agency, until the fragments of the ancient
ocean-bed, now the Downs, were lifted above the
reach of further destruction. The drainings of
the elevated portions of the soft calcareous rock
would then commence, and give rise to streams
and rills, by which the surface would be worn
into furrows and channels. Funnel-like cavities,
and deep and narrow cylindrical and tubular
hollows, would be formed by the gyratory action
of eddies or whirlpools, induced by opposing
currents ; such effects may be observed on the
muddy dunes of an estuary during the reces-
sion of the tide. The beds of loose and but
slightly water-worn flints — the undulated and
unbroken contour of the gently swelling hills —
and the smooth basin-shaped coombes, and valleys
of chalk districts — characters which are strikingly

* See Mr. Lyell on the elevation and denudation of the wealden districts ;
" Elements of Geology," vol. ii.


exemplified in the hills before us, would be the
natural result of such operations.

From Freshwater-Gate to Compton Bay.
— The road to Compton Bay sweeps round the
southern slope of Afton Down ; the pedestrian
should take the path along the edge of the cliff to
Compton Chine, where a narrow track leads to
the sea-shore. As we approach this spot a fine
view is obtained of the line of coast from the bay
to beyond Brook Point, as is shown in the slight
sketch, PL XI. The foreground is part of the
southern slope of Afton Down, consisting of
flinty chalk ; and the foot-track to the Chine is
seen crossing it on the right. The cliffs in this
view are composed of the clays, shales, and sands of
the Wealden, which continue to near Atherfield
Point. The nearest headland is Brook Point, the
western boundary of Brook Bay ; and the one im-
mediately beyond is the eastern limit of the same.
The ledges of rock extending from the foot of
Brook Point into the sea, are chiefly composed of
petrified trees. The most distant cape is part of
the greensand cliffs, near Blackgang Chine; and
the lofty range on the horizon is St. Catherines


Compton Chine is a deep chasm worn in the
ferruginous sands by a stream that falls from


the summit of the cliff; it is situated to the
west of the Blockade-station.

The footpath to the shore slopes along the face
of the crumbling cliffs of greensand strata, which
rise from beneath the upper divisions of the creta-
ceous system, as is shown in lign. 16. The succes-
sion of the beds from Freshwater to Compton Bay,
i. e. from west to east, is as follows : —

1 . Upper or flinty chalk.

2. Lower chalk.

3. Firestone, comprising the chalk marl.

4. Gait.

5. Greensand, consisting of beds of ferruginous saDds, clays,

sandstones, and layers of very compact ironstone grit.

6. AVealden clays, sands, shales, and limestones.

Geological sections of the southern
coast. — The strata incline to the west, as is
shown in lign. 16, to beyond Brook Chine,
where the eastern side of the anticlinal axis
begins, and the dip is to the east, as represented
in the continuation of the coast, in lign. 17.

This line of cliffs is, in fact, the counterpart of
that of Sandown Bay {ante, p. 134, lign. 9) ; but
the wealden deposits are here more developed,
and extend between six and seven miles along
the shore. As these cliffs consist of clays,
sandy marls, shales, and other materials that offer


but feeble resistance to the action of the waves,
the destruction effected by the sea during the
winter and early spring, when the highest tides
prevail, is very great; and the wealden fossils
washed out of the cliffs and strewn along these
shores are so numerous, that the strand between
Compton Bay and Atherfield has yielded a greater
number of fossil bones of colossal reptiles than
any other part of the Island. In short, these
strata and their organic remains impart to this
portion of the southern shore so much interest,
that it is desirable to postpone a particular account
of the wealden deposits for a special excursion to
Brook Bay. We will therefore continue our sur-
vey of the greensand by proceeding from Compton
to Atherfield, and along the Undercliff to San-
down Bay, where our investigation of the south
coast commenced.*

The chalk, firestone, and gait of Compton
Bay, are not very prolific in fossil remains ;
but the greensand yields ammonites, trigoniw,
pemce, &c. ; and numerous specimens of the
large oyster-like gryphea sinuata, (PL V. fig. 3,)
are generally scattered on the sands and shingle at
the foot of the cliffs. At the point where the

" The visitor who would find it more convenient to continue liis observa
tions along the cliff to Brook Chine, should refer to chapter ix.





lowermost bed of the greensand is in contact with
the wealden clays, the distinctive characters of the
marine and freshwater deposits may sometimes be
observed in a mass of the stratum but a few inches
thick ; marine shells appearing imbedded in the
upper layers, and freshwater shells in the lower

Pebbles and shingle. — Before we ascend the
cliff to pursue our excursion towards Atherfield,
I would offer a few remarks on the sea-beach.

The beds of shingle along this coast, consist in
a great measure of chalk flints that have been
broken and rounded by attrition into boulders,
pebbles, and gravel. This is evident from the
peculiar aspect and fracture of the stones, and the
nature of their organic remains, of which some
traces are generally manifest. The clear transparent
pebbles, with bands and veins of quartz and chal-
cedony, which in some specimens are as clear as
crystal, and in others of a bright yellow, amber,
dark brown, and bluish-black colour, have a
similar origin. The moss-agates,* as they are
called by the lapidaries, are silicified chalk
sponges ; and the beautiful fossils {Choanites)-\
commonly known as " petrified sea-anemones,' 1 '' are

• Not the German moss-agates exhibited in the shops as the genuine pro-
ductions of the Island. Sec note In page 18.
I " Thoughts on a Pebble," pi. 1 and 2.


characteristic zoophytes of the white chalk. Small
pebbles of pure transparent quartz or rock-crystal,
are often found in the shingle in Compton and
Sandown ; these have probably been washed out
of the wealden strata, for pebbles identical in
mineral ogical character occur in the grits of
Tilgate Forest and Tunbridge Wells.

But the shingle contains other siliceous pebbles
which essentially differ from those of the chalk-
flints. Some of these are composed of a dark
brown mottled jasper, and when cut and polished
resemble the well-known Egyptian pebbles ; others
are of an opaque white jasper, veined with black
dendritical or arborescent figures, or marked
with zones of rich brown tints. Some have a
concentric arrangement of bands of silex of
various shades of colour, and resemble agates ;
others assume the character of botroidal and
mammillated chalcedony.

The differences observable in the materials com-
posing the shingle, did not escape the notice of
Mr. Webster, who describes some of the principal
varieties of the pebbles, and suggests that those
which are not waterworn chalk-flints, may have
been derived from veins or nodular masses of
silex, in tertiary strata now destroyed. A polished
slice of silicified wood found in the shincde of


Sandown Bay, was presented to me by Mr. Fowl-
stone, of Ryde. I believe specimens of this kind
are very rare in the Island ; but on the western
coast of Sussex, waterworn fragments of silicified
monocotyledonous wood are occasionally met with.
Boulders and pebbles of petrified bone and
wood, and of shelly limestone, are common on
the beach in Compton and Sandown Bays ; they
are from the wealden beds, and will be more par-
ticularly noticed in a subsequent chapter.






From Compton Bay to Atherfield Point. —
The road from Compton Chine to the coast-guard
station at Atherfield Point, runs along the southern
flank of Shalcomb and Mottestone Downs. As
we pass Brook Manor-house the ferruginous beds
of greensand may be traced in the banks on the
road-side ; and Brook church is seen standing
high up the hill on a terrace of those deposits.
The relative positions of the strata in this district
are displayed in the cuttings on the sides of the
road from Shalcomb Down through the village of
Brook to the sea-shore ; as shown in lign. 18.
If we proceed from the coast at Brook Chine
through the village, and ascend the road by the
church, and over Shalcomb Down, we pass in suc-
cession, 1, the Wealden ; 2, the Greensand ; 3, the




Gait ; 4, the Firestone ; and then cross the ridge
formed by the highly inclined strata of the White-

Shalcomb Down.

Brook Puint

H. Fossil Trees. wealden. -6,


The turnpike-road leads through the villages of
Mottestone* and Brixton, to Shorwell, where it
divides, and sends off a branch to Newport on the
north-east, and another on the south-east, through
Kingston and Chale to Blaekgang Chine. About
midway between Brixton and Shorwell a tenantry
road turns off to the right, and admits a carriage
to within a few hundred yards of the cliff, near
the Atherfield Coast-guard Station. This is the
most convenient place to alight, and reach the
sea-shore near the junction of the Greensand and
Wealden formations. The path down the preci-
pitous face of the cliff lies a little to the east of the

* On an eminence overlooking the village of Mottestone is a rude pillar of
ferruginous sandstone called the "Long-Stone," and which was probably
erected ..* a landmark or boundary stone, at a very remote period. It is
twelve feet high ami of an irregular quadrangular form.


Station ; it is a mere foot-track worn in the rock
by the sailors and fishermen.* At a moderate
distance westward of the spot where the path
reaches the shore, is the headland called Ather-
field Point, on which stands the Station-house ;
and at its foot, a ledge of rocks extends into
the sea. Near this place after recent slips of
the cliff, and the removal of the fallen debris by
the waves, the uppermost of the Wealden deposits,
and the lowermost of the Greensand may be seen
in juxta-position; in other words, the line of de-
marcation between the accumulated sediments of
a mighty river — some primeval Nile or Ganges,
teeming with the spoils of the land and the ex-
uviae of extinct terrestrial and fluviatile animals
and plants — and the bed of a vast ocean, loaded
with the debris of marine organisms, of genera and
species unknown in the present seas.

Atherfield Cliffs. — These cliffs are about 150
feet high, and, with the exception of a few feet of
Wealden clay forming the base of the headland
above mentioned, entirely consist of the green-
sand strata, which extend eastward as far as the

* This path is too precipitous and inconvenient to be attempted without
risk by ladies or invalids. I have always visited the spot by this route, and
am not aware of there being a more easy descent to the beach, except at a
long distance from the most interesting part of the cliffs.

N 2


eye can reach. The total thickness of the series
is upwards of 800 feet ; but the section exposed,
though vertical, is in an oblique direction to the
planes of stratification, and from the slight angle
at which the strata dip to the north-east, the
cliffs as far as Blackgang Chine are composed of
the greensand deposits. To the eastward these
strata are concealed by the upper cretaceous
group along the Undercliff, reappear at Bon-
church Cove, and continue to Sandown, extend-
ing as far as the anticlinal axis of the Wealden in
the bay.

The lowermost bed which rests on the Wealden
at the base of Atherfield Point, is but a few feet
above the beach ; the uppermost strata first ap-
pear on the shore to the east of Rocken-end ;
between these two points the cliffs are made up of
sands and argillaceous deposits of various colours,
composition, and thickness, containing particular
collocations of organic remains. The importance
of the Atherfield section as elucidating the nature

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Online LibraryGideon Algernon MantellGeological excursions round the Isle of Wight, and along the adjacent coast of Dorsetshire; illustrative of the most interesting geological phenomena, and organic remains → online text (page 10 of 21)