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 4 of 21)
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teeth and palatal bones of Bays, and vertebrae of
osseous fishes, of species common in the clay of
Sheppey; also a portion of the carapace or buckler
of a freshwater turtle.'*

At Weybridge the banks show an example of
false stratification, as it is termed, of white and
fawn-coloured sands, with the usual capping of
gravel and clay. At Woking Common the Bag-

• Notice- of Fossils discovered in the Bagshot Sand at Goldsworth-hill,
Surrey) by the Rev. Dr. Backhaul. Proceeding* <>f the Geological Society of
London, vol. ii. p, 687.


shot sands still prevail, their sterile surface being-
covered with heather and broom, except in a few
places, where interspersions of clay produce ver-
dant spots, which appear like oases in the desert.
Greenish clays and marls, alternating with sand,
are next seen, and extensive plains clothed with
heather, and dotted with clumps of pines and firs.
Between Woking and Farnborough many sections
of the Bagshot sands are passed, and at the Wing-
field station the country presents the same geo-
logical character. Although from the rapidity of
our progress but transient glimpses can be ob-
tained of the adjacent district, yet the character
of the vegetation, and the appearance of the un-
enclosed tracts, destitute of all traces of habitation,
save a few solitary turf cabins, convey some idea
of the nature of the untractable soil produced by
these siliceous deposits. Such, indeed, is the
general aspect of sterility in the worst parts of
the Bagshot-heaths, that when the adjacent fertile
region is hidden from view, a stranger might sup-
pose himself transported to a desolate mountain
moor in the border countries.*

About three miles before we reach the station
at Basingstoke,-]- the Chalk emerges, and is seen

* Mr. Warburton on the Bagshot Sands, Geol. Trans, vol. i. p. 49.
t The picturesque ruins of the Chapel of the Holy Ghost, said to have been
erected temp. Edward IV., on the right of the station at Basingstoke, are


covered with a bed of tertiary sand; and at
Andovcr-road station the railway cutting exposes
a good section of the Upper-chalk, which now
continues, in greater or less thickness, surmounted
in some places by patches of tertiary clays, and
in others by gravel and loam, till we approach
Southampton, where it is wholly concealed by the
alluvial and eocene deposits. At the Winchester
station, which is on the chalk of the Hampshire.
downs, we have a fine view of the river valley, in
which stands the venerable city of the immortal
Alfred, hallowed by so many glorious associations
of the olden time ; and we catch a glimpse of that
precious monument of antiquity, the Hospital of
Saint Cross, with occasional views of the crystal
streams of the river Itchin, as they pursue their
tortuous course through the verdant chalk-valley
to Southampton-water.

Southampton station. — The accumulations
of alluvial gravel and loam around Southampton
are in many places of considerable thickness. The
organic remains hitherto discovered in these beds
are but few; comprising only some detached bones,
and a tooth of a mammoth, and bones of a species

worthy the notice of the traveller. An elegant hexagonal turret tower at

tlu- south-west, and part of the east ami south walls, are visible from the


of horse and deer; and as the tertiary strata are
in a great measure obscured by the superficial
deposits, there are no productive localities of
fossils in the immediate vicinity of Southampton.
The nature of the strata to a considerable depth,
has been ascertained by the borings lately under-
taken to obtain a more ample supply of water for
the inhabitants, than that yielded by the numerous
private wells in the town. These are sunk through
the bed of gravel which overlies the London clay,
to a depth of from 10 to 25 feet, this clay forming
the water shed or natural tank of the surrounding
district. At the railway station an Artesian well,
which overflows from a depth of 220 feet at the
rate of ten gallons per minute, was formed by
boring till the beds of sand of the plastic clay,
which lie between the London clay and the chalk,
were reached ; the water in this well rises, there-
fore, from the same geological source as the springs
near London.

A few years since it was resolved to obtain a
more copious and constant supply for the town,
by sinking an Artesian well on the Common. The
operations were commenced in 1838, and have
now reached a depth of 1,260 feet, at an expense
of 24,000/. The following is the section made
by the borings : —


Drift, or alluvial soil . . . . 38 feet.

London clay 304 * —

Plastic sands and clays ... 97 —

Chalk 821 —

This well yields by pumping 15,000 cubic feet of
water daily, but the quantity is only one half of
that required, and it will be necessary to continue
the borings till the firestone is reached (probably
a further depth of from 1 50 to 200 feet) before an
adequate flow of water is likely to be obtained.f
The impervious blue chalk-marl or gait, which
underlies the firestone, generally supports an abun-
dant sheet of water ; but whether a stream will
rise to the surface is extremely uncertain, and
depends on the level from which the water is
derived that feeds this subterranean reservoir, and
the condition of the basin which sustains \t.\

The branch of the South-western railway that
extends to Gosport, cuts through a few ridges of
tertiary clays, sands, and gravel, capped with drift,
but these present no sections of particular in-

• Many of the characteristic shells of these strata were brought up by the

t See an admirable Address on this subject to the Mayor of Southampton
and the Members of the Artesian Well Committee, by the Very Rev. Dr.
Bnckland; July, 1845. At the late meeting of the British Association of
Science at Southampton, the president, Sir Roderick Murchison, and several
other eminent geologists, examined the borings, and recommended the con-
tinuance of the operations till the firestone was reached.

; In the chalk districts of t he south-cast of Sussex copious streams of the
purest water rise from the junction of the grey mail with the white chalk.


terest.* At Stubbington, between four and five
miles west of Gosport, near which the line passes,
many interesting fossils have been obtained from
the tertiary clays and sands. -j-

Southampton to Ryde. — The steamers from
Southampton to the Isle of Wight generally touch
at East Cowes, and proceed to Ryde ; those from
Portsmouth cross Sjrithead to the latter town, the
distance being scarcely five miles. In the former
route we pass down Southampton-water, an arm of
the sea which extends ten miles inland in a north-
westerly direction, and separates the eastern part
of the coast of Hampshire from the New Forest
on the west. The entrance of Southampton-water
is guarded on the west by Calshot Castle, which
was erected by Henry VIII. on the narrow slip of
land that here advances some little distance from
the line of coast* We now obtain a distinct
view of the north side of the " beautiful Island ;"
and as we approach the land, two parallel chains
of hills may be observed, stretching in a direction
east and west through the whole extent of the
landscape. The nearest range is of moderate
height, and slopes towards the shore ; the distant

* Portsmouth and Gosport are built on eocene strata ; the wells penetrate
the London clay to the depth of from 200 to ouo feet.

t Several species of shells, collected by Mr. Holloway, of Portsmouth, are
figured in "Sowerby's Mineral Conchology."


chain, which bounds the horizon on the south',
rises with a bolder sweep, and to a much greater
elevation, and exhibits the smooth and rounded
aspect, and undulated outline, which are so cha-
racteristic of the mountain masses of the white
chalk, as to indicate their geological character,
even when seen from a considerable distance.
The first line of hills consists of freshwater strata,
which are superimposed on the eocene marine
deposits ; the distant range is part of the chain of
chalk downs that traverses the island throughout
its entire length, forming on the east the promon-
tory of Culver-cliff, and on the west that of the
Needles (see the map, PL XX.).

Geological structure of the Isle of Wight.
— Before we land, and proceed to examine par-
ticular localities, it will be necessary to take a
general view of the distribution of the three
formations of which the island consists. It is
shown in ligti. 3, (p. 75,) that the Solent and Spit-
head occupy a trough or channel from two to
seven miles wide-, formed by the London clay and
other tertiary deposits which lie upon the chalk.
The wells at Southampton, Portsmouth, &c, prove,
in the absence of natural sections, that although
the strata have undergone great disturbances, the
same order of superposition is maintained, as in


the south-east of England ; and in the southern
division of the Isle of Wight, where not only the
lowermost cretaceous strata, but even the wealclen,
rise to the surface, in consequence of the highly
inclined position into which the central mass of
rocks has been thrown, the natural order of the
deposits is not inverted.*

The Isle of Wight is of an irregular rhomboidal
form, being in length, from east to west, twenty-
three miles, and from north to south, in the widest
part, thirteen miles ; the circumference is between
seventy and eighty miles. Its surface comprises
about 105,000 acres, of which 75,000 acres are
under tillage, 20,000 acres are pasturage, and
10,000 acres unproductive heaths and commons.
The population is estimated at nearly 45,000.

The map, PL XX, shows the range and extent
of the respective formations which lie beneath the
vegetable soil and superficial loam and gravel. The
section in the same plate represents a vertical cut
through the island, from Cowes on the north, to
the sea-shore beyond St. Catherine's down on the
south, and exhibits the relative position and direc-

* The Underclitl" presents an apparent exception, for in some instances
masses of white chalk are seen covered with beds of firestnne, marl, and
gait ; hut these are merely portions of the cliffs that have fallen down in a
retroverted position from the encroachments of the sea in comparatively very
modern periods.



tion of the principal deposits ; these are further
exemplified by the instructive diagram, PL VII,
p. 94.

By a reference to the map it will be seen that
the eocene strata which were deposited on the
chalk when the latter was in a horizontal position
(lign. 2, p. 74), form the northern division of the
island ; this tract of country is coloured pink.

The other portion (coloured blue) is almost en-
tirely composed of the different members of the
cretaceous system. The white-chalk forms a range
of downs from the eastern to the western extre-
mity, and is flanked on the south by the lower
beds of this formation. These are succeeded by
another group of chalk-hills, that expands into a
broad and lofty promontory, in some parts be-
tween 800 and 900 feet high, crested by St. Cathe-
rine's, Boniface, and Shanklin downs. On the
southern escarpment of this chain the inferior
deposits of the cretaceous system reappear, and
fallen masses of these rocks form the irregular
line of terraces which constitute the Undercliff.
The downs on the southern coast are separated
from those inland by an anticlinal axis which
extends through this part of the Island, and is
produced by the upheaval of the firestone, gait,
and greensand. Tins is shown by the section


from north to south given in the map (PL XX), in
which the different members of the chalk forma-
tion are denned by variations in the lines of shading,
as explained in the index of colours.

The promontory of the Undercliff is flanked
both on the east and west by extensive bays,
which have been excavated in the clays and sands
of the wealden and inferior cretaceous deposits,
by the long continued encroachments of the sea.
The wealden (coloured sienna on the map) occu-
pies an inconsiderable extent of surface ; but in
Sandown bay on the east, and in Brixton, Brook,
and Compton bays on the west, the cliffs, which
are formed of the upper clays and sands of this for-
mation, are exposed to unremitting destruction
from the action of the waves. The sea-shore is,
therefore, strewn with the detritus of these fluvia-
tile strata, and the shingle contains innumerable
water-worn fragments of the bones of reptiles, and
other organic remains.

That the general reader may obtain an accurate
idea of the phenomena above described, the dia-
gram, PL VII, for which I am indebted to my
friend Professor John Phillips, is subjoined. In
this plan the geographical features of the island
are intentionally exaggerated, that the most im-
portant physical characters may be clearly under-

* a

£ O

= ,§



stood. The northern district, consisting of fresh-
water and marine eocene deposits, is marked
tertiary. The chalk downs are seen in their full
extent from east to west, the dotted lines denoting
the inclined direction of the strata as indicated
by the layers of flint nodules ; and the lower mem-
bers of the cretaceous system occupy the southern
portion of the Island ; the principal subdivisions,
viz. the firestone (/.), gait (g.), and greensand (g*s.),
being marked with letters of reference. The
wealden strata (w.) are shown in the bays on the
east and west of the Undercliff. The vertical cut
or section through jlie island from north to south,
explains the position and flexures of the strata,
which have given rise to the present geological
characters of the surface of the country ; the
wealden constituting the foundation and central
axis of the Island.

Rivers and Streams. — There is a good supply
of water, at a moderate depth, throughout,, the
greater part of the less elevated districts ; but the
rivers and streams are neither numerous nor con-
siderable. The drainage of the country is chiefly
effected by four or five rivers that flow from the
northern flanks of the chalk downs. Of these,
the principal is the Medina, which, rising at the
north-eastern base of St. Catherine's-hill, meanders


along the valley that runs to the east of Gat-
combe and Mount joy. The river flows on to the
east of the town of Newport, and soon expands
into a wide estuary, which opens into the sea on
the north ; the towns of East and West Cowes
being situated on the banks of the embouchure
of the river.

Between Ryde and Cowes there is an estuary
fed by springs that issue from the northern
foot of Arreton and Ashey downs, and form a
considerable breadth of water at Wooton-bridge,
called Wooton-river ; the estuary below the bridge
communicates with the sea, and is termed Fish-

The most considerable estuary of the Island is
Brading Haven, which covers 800 acres, and at
high water has the aspect of a beautiful lake ; but
during low water it is a muddy swamp, through
which meanders an inconsiderable river, called the
Eastern Yar, originating in springs that rise at the
foot of the chalk range near Godshill.

Newtown Bay, between Cowes and Yarmouth,
is the mouth of a small river of the same name,
which is mainly fed by a copious stream that
rises near Calbourne.

The Western Yar has its source from springs
that burst forth from the foot of the chalk near


Freshwater, within a short distance of the southern
shore, and quickly expands into an estuary that
falls into the sea at Yarmouth, the entire length
of the river scarcely exceeding three miles.

Along the southern shore of the Island there
are no streams sufficiently large to deserve the
name of rivers ; but the clay beds that in some
parts of the cliffs are covered by porous strata
many "yards in thickness, give rise to copious
rivulets, some of which issue from a great height,
and dashing from ledge to ledge, fall into the sea
in cascades of considerable picturesque beauty;
those of Shanklin and Blackgang Chines {PL XIII.)
are well known examples.

From Cowes to Ryde. — From the highly
cultivated state of that portion of the Island we are
approaching, and the luxuriant woods and copses
with which it is adorned, its geological structure is
almost wholly concealed from view. The water-
worn blocks of limestone on the sea-shore, and
the layers of tertiary strata exposed in those
places where recent encroachments of the sea
have undermined the low cliffs which skirt the
plantations along the water's edge, afford, how-
ever, indications of the nature of the deposits
composing this district. As there are no loca-
lities of geological interest around Cowes that are


accessible to strangers, we proceed to Ryde, the
quarries at Binstead in the vicinity of that town
exhibiting good sections of the freshwater strata,
which extend through the island from Headon-
hill on the west, to St. Helen's and Bembridge
on the east. On landing at Ryde pier, if at the
recession of the tide, it will be instructive to notice
the appearance of the surface of the sand and
silt that extend along the shore, for it is often
deeply impressed with ripple-marks produced by
the action of the waves ; and similar appearances
will be presented to our notice on the slabs of
limestone, and laminated clays and shales of the
wealden, and other ancient deposits.*

The sea-shore at Ryde, during the last century,
has undergone a remarkable change in its geolo-
gical character, which is worthy of attention. Sir
Henry Englefieldf states that, "when Fielding,
in the year 1753, was at Ryde, on his voyage to
Lisbon, the town was totally inaccessible except

On a late visit to Ryde, the wind having ;t few hours previously been
exceedingly variable, 1 found the ripple-marks formed on the surface of the
muddy dunes by the agitated waters of a very remarkable character, and
strikingly resembling the appearance of the limestone covered with fossil
fuei. from the Alleghany Mountains: and shortly afterwards 1 obtained from
I 111 W I allien at Sandown-bay a slab of shelly marble, with the upper-surface
rippled in precisely a similar manner.

I " Descriptions of the Picturesqui Bi nth Intiquitie , and Geological
Phenomena ol the Isle of Wight," bj Sir Henrj ('. Englefleld, Bart. 18 1C

p. 16.


at or near high water, as the tide on its recession
left a vast breadth of mud, which was too soft to
bear the lightest weight. But this mud-bank is
now almost covered by a layer of fine white sand,
which has formed a surface smooth and firm
enough to bear wheel-carriages, and which renders
bathing at all times safe and agreeable. This bed
of sand reaches to Binstead, having, during the
last fifty years, covered two miles of the shore ;
and it is said to be still extending to the west-
ward. To what cause this change is owing it is
difficult to explain ; but it is an example of an
alternation of deposits from the action of the sea
in circumstances apparently unchanged."



Freshwater eocene strata. — The most remark-
able peculiarity in the eocene formation of the
Isle of Wight as compared with that of London,
consists in the lacustrine and fluviatile character
of the upper series of deposits, which are super-
imposed on marine strata identical with those of
the metropolis. For though in some localities
clays and sands containing marine and estuary
shells, alternate with marls and limestones abound-
ing in fluviatile species ; and in others the strata
are fluvio-marine, that is, contain an intermixture
of marine and freshwater shells ; yet throughout
a considerable thickness of deposits the organic
remains are entirely fluviatile and terrestrial. In
tli is respect the tertiary system of the Island cor-
responds with that of the Paris basin, which is
characterised by alternations of freshwater marls,


gypseous limestones, and siliceous millstones, with
marine sands and clays. It was from the gypsum
quarries of Montmartre that those relics of ex-
tinct mammalia were obtained, which the genius
of the illustrious Cuvier called forth from their
rocky sepulchres, and invested anew with the
forms and lineaments of life.*

In the Isle of Wight the freshwater series con-
sists of marls, limestones, and shelly concretions,
with intercalations of clay, marl, and sand; the
gypseous marls and limestones, and the siliceous
millstones of the Paris group are altogether want-
ing. Nevertheless, there is evidence that the two
formations were contemporaneous, for the relics of
Cuvierian pachydermata have been discovered in
the Binstead limestones (see PI. II.).

The freshwater eocene strata of the Island, which
are spread over the whole of the northern part,
are denoted on the map {PI. XX.) by pink on a
plain ground ; the marine beds appear on the
surface as a narrow band extending along the
northern flank of the chalk downs, and are in-
dicated by the same colour on a ground shaded
with parallel lines. The localities which exhibit
the most instructive sections of the marine and
freshwater deposits in their natural order of

* Wonders of Geology, vol. i. p. 240.


superposition arc Headon Hill, Alum Bay, and
Whitecliff Bay.

Binstead quarries.- — The limestones in the
vicinity of Hyde have been quarried for many
centuries ; the shelly, as well as the compact
varieties, having been in great demand during the
middle ages for building.* Though the sections
exposed in the quarries now open are inconside-
rable, they will suffice to illustrate the characters
of the strata and the nature of their fossils, and
render the interpretation of the phenomena here-
after to be examined more easy of comprehension.
I would, therefore, first conduct the reader to
Binstead, which lies about a mile to the west of
Ryde. There are several quarries on both sides
of the turnpike road to Newport, and others in a
field which lies on the left of the footpath that
turns oil" from the main road just beyond a Doric
lodge, and leads by copses and hedge-rows to the
picturesque hamlet of Binstead, affording here
and there glimpses of the most charming rural
scenery. The quarries for the extraction of the
stone vary in depth from ten to twenty feet, and

* A great part of Winchester Cathedra] is built of stone from the old
quarries at Binstead. Some- of tin- walls of Lewes Priory were faced with
this -lone; and several ancient Sussex churches an- in part constructed of it.
ii tj composed of comminuted shells, held together by a sparry calca-
reous cement, was extensivel] used; it has been frequently mistaken for
Caen stone by our antiquaries.


appear to have been opened without regard to any
regular plan, wherever it was thought a layer of
compact stone could be easily reached.*

Fossil rein- deer. — Upon entering a quarry at
Binstead, the dislocated state of the beds of lime-
stone immediately strikes the observer. Vertical
and diagonal fissures and chasms, extending in
some places to the depth of fifteen feet, are seen
traversing the solid rock, and filled with the
alluvial loam and clay that form the general sub-
soil of this district ; in these deposits bones of a
species of horse and ox have been discovered. On
a recent visit, I obtained a considerable portion
of the skull of a Rein-deer (Cervus tarandus), from
clay occupying the bottom of a vertical fissure at
the depth of ten feet from the surface. It con-
sists of the posterior part of the cranium, and
closely resembles a specimen found in a cavern at
Berryhead, in Devonshire, and figured by Pro-
fessor Owen in British Mammalia ;f the latter is
referred by that eminent palaeontologist to the
recent species of Rein-deer, chiefly from the proxi-
mity of the bases of the antlers to the occipital

* Quarr Abbey. — In a sequestered valley, within a short distance of Bin-

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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 4 of 21)