The chalk formations or “cretaceous group of beds” include strata of
various mineral substances; but the white chalk which forms the cliffs
of Dover and the adjoining coasts, and the downs and chalk quarries of
the South of England, is the chief and most characteristic formation.
Chalk, immense as are the masses in which it has been deposited, owes
its origin to living actions; every particle of it once circulated in
the blood or vital juices of certain species of animals, or of a few
plants, that lived in the seas of the secondary period of geological
time. White chalk consists of carbonate of lime, and is the result of
the decomposition chiefly of coral-animals (_Madrepores_, _Millepores_,
_Flustra_, _Cellepora_, &c.), of sea-urchins (_Echini_), and of
shell-fishes (_Testacea_), and of the mechanical reduction, pounding,
and grinding of their shells. Such chalk-forming beings still exist, and
continue their operations in various parts of the ocean, especially in
the construction of coral reefs and islands.
Every river that traverses a limestone district carries into the sea a
certain proportion of caustic lime in solution: the ill effects of the
accumulation of this mineral are neutralised by the power allotted to
the above-cited sea-animals to absorb the lime, combine it with
carbonic-acid, and precipitate or deposit it in the condition of
insoluble chalk, or carbonate of lime.
The entire cretaceous series includes from above downwards:
Maestricht beds of yellowish chalk.
Upper white chalk with flints.
Lower white chalk without flints.
Upper green-sand.
Gault.
Lower green-sand and Kentish rag.
The best known and most characteristic large extinct animal of the chalk
formations is chiefly found in the uppermost and most recent division,
and is called
No. 1.—The Mosasaurus.
(_Mosasaurus Hoffmanni_, Hoffmann’s Mosasaur.)
Of this animal almost the entire skull has been discovered, but not
sufficient of the rest of the skeleton to guide to a complete
restoration of the animal. The head only, therefore, is shown, of the
natural size, at the left extremity of the Secondary Island.
The first or generic name of this animal is derived from the locality,
Maestricht, on the river Meuse (Lat. _Mosa_), in Germany, where its
remains have been chiefly discovered, and from the Greek word _sauros_,
a lizard, to which tribe of animals it belongs. Its second name refers
to its discoverer, Dr. Hoffmann, of Maestricht, surgeon to the forces
quartered in that town in 1780. This gentleman had occupied his leisure
by the collection of the fossils from the quarries which were then
worked to a great extent at Maestricht for a kind of yellowish stone of
a chalky nature, and belonging to the most recent of the secondary class
of formations in geology. In one of the great subterraneous quarries or
galleries, about five hundred paces from the entrance, and ninety feet
below the surface, the quarrymen exposed part of the skull of the
Mosasaurus, in a block of stone which they were engaged in detaching. On
this discovery they suspended their work, and went to inform Dr.
Hoffmann, who, on arriving at the spot, directed the operations of the
men, so that they worked out the block without injury to the fossil; and
the doctor then, with his own hands, cleared away the matrix and exposed
the jaws and teeth, casts of which are shown in the cretaceous rock of
the Island.
This fine specimen, which Hoffmann had added with so much pains and care
to his collection, soon, however, became a source of chagrin to him. One
of the canons of the cathedral at Maestricht, who owned the surface of
the soil beneath which was the quarry whence the fossil had been
obtained, when the fame of the specimen reached him, pleaded certain
feudal rights to it. Hoffmann resisted, and the canon went to law. The
Chapter supported the canon, and the decree ultimately went against the
poor surgeon, who lost both his specimen and his money—being made to pay
the costs of the action. The canon did not, however, long enjoy
possession of the unique specimen. When the French army bombarded
Maestricht in 1795, directions were given to spare the suburb in which
the famous fossil was known to be preserved; and after the capitulation
of the town it was seized and borne off in triumph. The specimen has
since remained in the museum of the Garden of Plants at Paris.
This skull of the Mosasaurus measures four and a half feet long and two
and a half feet wide. The large pointed teeth on the jaws are very
conspicuous; but, in addition to these, the gigantic reptile had teeth
on a bone of the roof of the mouth (the pterygoid), like some of the
modern lizards. The entire length of the animal has been estimated at
about thirty feet. It is conjectured to have been able to swim well, and
to have frequented the sea in quest of prey: its dentition shows its
predatory and carnivorous character, and its remains have hitherto been
met with exclusively in the chalk formations. Besides the specimens from
St. Peter’s Mount, Maestricht, of which the above-described skull is the
most remarkable, fossil bones and teeth of the Mosasaurus have been
found in the chalk of Kent, and in the green-sand—a member of the
cretaceous series—in New Jersey, United States of America. No animal
like the Mosasaurus is now known to exist.
Nos. 2 & 3.—The Pterodactyle.
Nos. 2 and 3 are restorations of a flying reptile or dragon, called
Pterodactyle, from the Greek words _pteron_, a wing, and _dactylos_, a
finger; because the wings are mainly supported by the outer finger,
enormously lengthened and of proportionate strength, which,
nevertheless, answers to the little finger of the human hand. The wings
consisted of folds of skin, like the leather wings of the bat; and the
Pterodactyles were covered with scales, not with feathers: the head,
though somewhat resembling in shape that of a bird, and supported on a
long and slender neck, was provided with long jaws, armed with teeth;
and altogether the structure of these extinct members of the reptilian
class is such as to rank them amongst the most extraordinary of all the
creatures yet discovered in the ruins of the ancient earth.
Remains of the Pterodactyle were first discovered, in 1784, by Prof.
Collini, in the lithographic slate of Aichstadt, in Germany, which slate
is a member of the oolitic formations: the species so discovered was at
first mistaken for a bird, and afterwards supposed to be a large kind of
bat, but had its true reptilian nature demonstrated by Baron Cuvier, by
whom it was called the _Pterodactylus longirostris_, or Long-beaked
Pterodactyle: it was about the size of a curlew.
A somewhat larger species—the _Pterodactylus macronyx_, or Long-clawed
Pterodactyle—was subsequently discovered by the Rev. Dr. Buckland, in
the lias formation of Lyme Regis: its wings, when expanded, must have
been about four feet from tip to tip. The smallest known species—the
_Pterodactylus brevirostris_, or Short-beaked Pterodactyle—was
discovered in the lithographic slate at Solenhofen, Germany, and has
been described by Professor Soemmering.
Remains of the largest known kinds of Pterodactyle have been discovered
more recently in chalk-pits, at Burham, in Kent. The skull of one of
these species—the _Pterodactylus Cuvieri_—was about twenty inches in
length, and the animal was upborne on an expanse of wing of probably not
less than eighteen feet from tip to tip. The restored specimen of this
species is numbered 3.
A second very large kind of Pterodactyle—the _Pterodactylus
compressirostris_, or Thin-beaked Pterodactyle—had a head from fourteen
to sixteen inches in length, and an expanse of wing, from tip to tip, of
fifteen feet. The remains of this species have also been found in the
chalk of Kent. From the same formation and locality a third large kind
of Pterodactyle, although inferior in size to the two foregoing, has
been discovered, called the _Pterodactylus conirostris_, and also—until
the foregoing larger kinds were discovered—_Pterodactylus giganteus_.
The long, sharp, conical teeth in the jaws of the Pterodactyles indicate
them to have preyed upon other living animals; their eyes were large, as
if to enable them to fly by night. From their wings projected fingers,
terminated by long curved claws, and forming a powerful paw, wherewith
the animal was enabled to creep and climb, or suspend itself from trees.
It is probable, also, that the Pterodactyles had the power of swimming;
some kinds, _e.g._, the _Pterodactylus Gemmingi_, had a long and stiff
tail. “Thus,” writes Dr. Buckland, “like Milton’s Fiend, all qualified
for all services and all elements, the creature was a fit companion for
the kindred reptiles that swarmed in the seas, or crawled on the shores
of a turbulent planet.
‘The Fiend,
O’er bog, or steep, through strait, rough, dense, or rare,
With head, hands, wings, or feet, pursues his way,
And swims, or sinks, or wades, or creeps, or flies.’
_Paradise Lost_, Book II.”