The Wealden is a mass of petrified clay, sand, and sandstone, deposited
from the fresh or brackish water of probably some great estuary, and
extending over parts of the counties of Kent, Surrey, and Sussex. This
fresh-water formation derives its name from the “Weald” or “Wold” of
Kent, where it was first geologically studied, and where it is exposed
by the removal of the chalk, which covers or overlies it, in other parts
of the South of England.
The Wealden is divided into three groups of strata, which succeed each
other in the following descending order:—
1st. Weald Clay, sometimes including thin beds of sand and shelly
limestone, forming beds of from 140 to 280 feet in depth or vertical
thickness.
2nd. Hastings Sand, in which occur some clays and calcareous grits,
forming beds of from 400 to 500 feet in depth.
3rd. Purbeck Beds, so called from being exposed chiefly in the Isle of
Purbeck, off the coast of Dorsetshire, where it forms the quarries of
the limestone for which Purbeck is famous: the beds of limestones and
marls are from 150 to 200 feet in depth.
Nos. 4 & 5.—The Iguanodon.
(_Iguanodon Mantelli_, Conybeare.)
One afternoon, in the spring of 1822, an accomplished lady, the wife of
a medical practitioner, at Lewes, in Sussex, walking along the
picturesque paths of Tilgate Forest, discovered some objects in the
coarse conglomerate rock of the quarries of that locality, which, from
their peculiar form and substance, she thought would be interesting to
her husband, whose attention had been directed, during his professional
drives, to the geology and fossils of his neighbourhood.
The lady was Mrs. Mantell: her husband, the subsequently distinguished
geologist, Dr. Mantell,[2] perceived that the fossils discovered by his
wife were teeth, and teeth of a large and unknown animal.
“As these teeth,” writes the doctor, “were distinct from any that had
previously come under my notice, I felt anxious to submit them to the
examination of persons whose knowledge and means of observation were
more extensive than my own. I therefore transmitted specimens to some of
the most eminent naturalists in this country and on the continent. But
although my communications were acknowledged with that candour and
liberality which constantly characterise the intercourse of scientific
men, yet no light was thrown upon the subject, except by the illustrious
Baron Cuvier, whose opinions will best appear by the following extract
from the correspondence with which he honoured me:—
“‘These teeth are certainly unknown to me; they are not from a
carnivorous animal, and yet I believe that they belong, from their
slight degree of complexity, the notching of their margins, and the thin
coat of enamel that covers them, to the order of reptiles.
“‘May we not here have a new animal!—a herbivorous reptile? And, just as
at the present time with regard to mammals (land-quadrupeds with warm
blood), it is amongst the herbivorous that we find the largest species,
so also with the reptiles at the remote period when they were the sole
terrestrial animals, might not the largest amongst them have been
nourished by vegetables?
“‘Some of the great bones which you possess may belong to this animal,
which, up to the present time, is unique in its kind. Time will confirm
or confute this idea, since it is impossible but that one day a part of
the skeleton, united to portions of jaws with the teeth, will be
discovered.’”
“These remarks,” Dr. Mantell proceeds to say, “induced me to pursue my
investigations with increased assiduity, but hitherto they have not been
attended with the desired success, no connected portion of the skeleton
having been discovered. Among the specimens lately connected, some,
however, were so perfect, that I resolved to avail myself of the
obliging offer of Mr. Clift (to whose kindness and liberality I hold
myself particularly indebted), to assist me in comparing the fossil
teeth with those of the recent Lacertæ in the Museum of the Royal
College of Surgeons. The result of this examination proved highly
satisfactory, for in an Iguana which Mr. Stutchbury had prepared to
present to the College, we discovered teeth possessing the form and
structure of the fossil specimens.” (Phil. Trans., 1825, p. 180.) And he
afterwards adds:—“The name Iguanodon, derived from the form of the
teeth, (and which I have adopted at the suggestion of the Rev. W.
Conybeare,) will not, it is presumed, be deemed objectionable.” (Ib. p.
184.)
The further discovery which Baron Cuvier’s prophetic glance saw buried
in the womb of time, and the birth of which verified his conjecture that
some of the great bones collected by Dr. Mantell belonged to the same
animal as the teeth, was made by Mr. W. H. Bensted, of Maidstone, the
proprietor of a stone-quarry of the Shanklin-sand formation, in the
close vicinity of that town. This gentleman had his attention one day,
in May, 1834, called by his workmen to what they supposed to be
petrified wood in some pieces of stone which they had been blasting. He
perceived that what they supposed to be wood was fossil bone, and with a
zeal and care which have always characterised his endeavours to secure
for science any evidence of fossil remains in his quarry, he immediately
resorted to the spot. He found that the bore or blast by which these
remains were brought to light, had been inserted into the centre of the
specimen, so that the mass of stone containing it had been shattered
into many pieces, some of which were blown into the adjoining fields.
All these pieces he had carefully collected, and proceeding with equal
ardour and success to the removal of the matrix from the fossils, he
succeeded after a month’s labour in exposing them to view, and in
fitting the fragments to their proper places.
This specimen is now in the British Museum.
Many other specimens of detached bones, including vertebræ or parts of
the back-bone, especially that part resting on the hind limbs, and
called the “pelvis,” bones of the limbs, down to those that supported
the claws, together with jaws and teeth, which have since been
successively discovered, have enabled anatomists to reconstruct the
extinct Iguanodon, and have proved it to have been a herbivorous
reptile, of colossal dimensions, analogous to the diminutive Iguana in
the form of its teeth, but belonging to a distinct and higher order of
reptiles, more akin to the crocodiles. The same rich materials,
selecting the largest of the bones as a standard, have served for the
present restorations (Nos. 4 and 5) of the animal, as when alive: all
the parts being kept in just proportion to the standard bones, and the
whole being thus brought to the following dimensions:—
Total length, from the nose or muzzle 34 feet 9 inches.
to the end of the tail
Greatest girth of the trunk 20 ” 5 ”
Length of the head 3 ” 6 ”
Length of the tail 15 ” 6 ”
The character of the scales is conjectural, and the horn more than
doubtful, though attributed to the Iguanodon by Dr. Mantell and most
geologists.
This animal probably lived near estuaries and rivers, and may have
derived its food from the _Clathrariæ_, _Zamiæ_, _Cycades_, and other
extinct trees, of which the fossil remains abound in the same formations
as those yielding the bones and teeth of the Iguanodon.
These formations are the Wealden and the Neocomian or green-sand: the
localities in which the remains of the Iguanodon have been principally
found, are the Weald of Kent and Sussex: Horsham, in Sussex; Maidstone,
in Kent; and the Isle of Wight.
Restorations of the _Cycas_ and _Zamia_ are placed, with the Iguanodon,
on the Wealden division of the Secondary Island.