English equivalents. French classification.
Lower Greensand, upper part. Étage Aptien st.
Lower Greensand, lower part. „ Néocomien supérieur.
Weald clay and Hastings sands. „ Néocomien inférieur.
The Lower Wealden or Hastings Sand consists of sand, sandstone, and
calciferous grit, clay, and shale, the argillaceous strata
predominating. This part of the Wealden consists, in descending order,
of:--
Feet.
Tunbridge Wells sand--Sandstone and loam 150
Wadhurst clay--Blue and brown shale and clay, with a little
calc grit 100
Ashdown sands--Hard sand, with beds of calc grit 160
Ashburnham sands--Mottled, white, and red clay and sandstone 330
The Hastings sand has a hard bed of white sand in its upper part, whose
steep natural cliffs produce the picturesque scenery of the “High rocks”
of Hastings in Sussex.
Calcareous sandstone and grit, in which Dr. Mantell found the remains of
the _Iguanodon_ and _Hylæosaurus_, form an upper member of the
Tunbridge Wells Sand. The formation extends over Hanover and Westphalia;
the Wealden of these countries, according to Dr. Dunker and Von Meyer,
corresponding in their fossils and mineral characters with those of the
English series. So that “we can scarcely hesitate,” says Lyell, “to
refer the whole to one great delta.”[78]
[78] Lyell’s “Elements of Geology,” p. 349.
The overlying Weald clay crops out from beneath the Lower Greensand in
various parts of Kent and Sussex, and again in the Isle of Wight, and in
the Isle of Purbeck, where it reappears at the base of the chalk.
The upper division (or the Weald clay) is, as we have said, of purely
fresh-water origin, and is supposed to have been the estuary of some
vast river which, like the African Quorra, may have formed a delta some
hundreds of miles broad, as suggested by Dr. Dunker and Von Meyer.
The Lower Greensand is known, also, as the _Néocomien_, after Neocomium,
the Latin name of the city of Neufchatel, in Switzerland, where this
formation is largely developed, and where, also, it was first recognised
and established as a distinct formation. Dr. Fitton, in his excellent
monograph of the Lower Cretaceous formations, gives the following
descending succession of rocks as observable in many parts of Kent:--
Feet.
1. Sand, white, yellowish, or brown, with concretions
of limestone and chert 70
2. Sand, with green matter 70 to 100
3. Calcareous stone, called Kentish rag 60 to 80
These divisions, which are traceable more or less from the southern part
of the Isle of Wight to Hythe in Kent, present considerable variations.
At Atherfield, where sixty-three distinct strata, measuring 843 feet,
have been noticed, the limestone is wholly wanting, and some fossils
range through the whole series, while others are confined to particular
divisions; but Prof. E. Forbes states, that when the same conditions are
repeated in overlying strata the same species reappear; but that changes
of depth, or of the mineral nature of the sea-bottom, the presence or
absence of lime or of peroxide of iron, the occurrence of a muddy,
sandy, or gravelly bottom, are marked by the absence of certain species,
and the predominance of others.[79]
[79] Ibid, p. 340.
Among the marine fauna of the Néocomian series the following are the
principal. Among the _Acephala_, one of the largest and most abundant
shells of the lower Néocomian, as displayed in the Atherfield section,
is the large _Perna Mulleti_ (Fig. 131).
[Illustration: Fig. 131.--Perna Mulleti. One-quarter natural size.
_a_, exterior; _b_, part of the upper hinge.]
[Illustration: Fig. 132.--Hamites. One-third natural size.]
The _Scaphites_ have a singular boat-shaped form, wound with contiguous
whorls in one part, which is detached at the last chamber, and projects
in a more or less elongated condition.
_Hamites_, _Crioceras_, and _Ancyloceras_ have club-like terminations
at both extremities; they may almost be considered as non-involuted
Ammonites with the spiral evolutions disconnected or partially unrolled,
as in the engraving (Figs. 125 and 132). _Ancyloceras Matheronianus_
seems to have had spines projecting from the ridge of each of the
convolutions.
[Illustration: Fig. 133.--Shell of Turritella terebra.
(Living form.)]
[Illustration: Fig. 134.--Turrillites costatus.
(Chalk.)]
The _Toxoceras_ had the shell also curved, and not spiral.
The _Baculites_ had the shell differing from all Cephalopods, inasmuch
as it was elongated, conical, perfectly straight, sometimes very
slender, and tapering to a point.
The _Turrilites_ have the shell regular, spiral, and _sinistral_; that
is, turning to the left in an oblique spiral of contiguous whorls. The
engraving will convey the idea of their form (Fig. 134).
Among others, as examples of form, we append Figs. 133, 135, 136.
This analysis of the marine fauna belonging to the Néocomian formation
might be carried much further, did space permit, or did it promise to be
useful; but, without illustration, any further merely verbal description
would be almost valueless.
[Illustration: Fig. 135--Terebrirostra lyra.
_a_, back view; _b_, side view.]
[Illustration: Fig. 136.--Terebratula deformis.]
Numerous Reptiles, a few Birds, among which are some “Waders,” belong to
the genera of _Palæornis_ or _Cimoliornis_; new Molluscs in considerable
quantities, and some extremely varied Zoophytes, constitute the rich
fauna of the Lower Chalk. A glance at the more important of these
animals, which we only know in a few mutilated fragments, is all our
space allows; they are true medals of the history of our globe, medals,
it is true, half effaced by time, but which consecrate the memory of
departed ages.
In the year 1832 Dr. Mantell added to the wonderful discoveries he had
made in the Weald of Sussex, that of the great Lizard-of-the-woods, the
_hylæosaurus_ (ὑλη, _wood_, σαυρος, _lizard_). This discovery was made
in Tilgate forest, near Cuckfield, and the animal appears to have been
from twenty to thirty feet in length. The osteological characters
presented by the remains of the Hylæosaurus are described by Dr. Mantell
as affording another example of the blending of the Crocodilian with the
Lacertian type of structure; for we have, in the pectoral arch, the
scapula or omoplate of a crocodile associated with the coracoid of a
lizard. Another remarkable feature in these fossils is the presence of
the large angular bones or spines, which, there is reason to infer,
constituted a serrated crest along the middle of the back; and the
numerous small oval dermal bones which appear to have been arranged in
longitudinal series along each side of the dorsal fringe.
The _Megalosaurus_, the earliest appearance of which is among the more
ancient beds of the Liassic and Oolitic series, is again found at the
base of the Cretaceous rocks. It was, as we have seen, an enormous
lizard, borne upon slightly raised feet; its length exceeded forty feet,
and in bulk it was equal to an elephant seven feet high.
[Illustration: Fig. 137.--Lower Jaw of the Megalosaurus.]
[Illustration: Fig. 138.--Tooth of Megalosaurus.]
The Megalosaurus found in the ferruginous sands of Cuckfield, in Sussex,
in the upper beds of the Hastings Sands, must have been at least sixty
or seventy feet long. Cuvier considered that it partook both of the
structure of the Iguana and the Monitors, the latter of which belong to
the Lacertian Reptiles which haunt the banks of the Nile and tropical
India. The Megalosaurus was probably an amphibious Saurian. The
complicated structure and marvellous arrangement of the teeth prove that
it was essentially carnivorous. It fed probably on other Reptiles of
moderate size, such as the Crocodiles and Turtles which are found in a
fossil state in the same beds. The jaw represented in Fig. 137 is the
most important fragment of the animal we possess. It is the lower jaw,
and supports many teeth: it shows that the head terminated in a straight
muzzle, thin and flat on the sides, like that of the _Gavial_, the
Crocodile of India. The teeth of the Megalosaurus were in perfect accord
with the destructive functions with which this formidable creature was
endowed. They partake at once of the nature of a knife, sabre, and saw.
Vertical at their junction with the jaw, they assume, with the increased
age of the animal, a backward curve, giving them the form of a
gardener’s pruning-knife (Fig. 138; also _c._ Fig. 179). After
mentioning some other particulars, respecting the teeth, Buckland says:
“With teeth constructed so as to cut with the whole of their concave
edge, each movement of the jaws produced the combined effect of a knife
and a saw, at the same time that the point made a first incision like
that made by a point of a double-cutting sword. The backward curvature
taken by the teeth at their full growth renders the escape of the prey
when once seized impossible. We find here, then, the same arrangements
which enable mankind to put in operation many of the instruments which
they employ.”
[Illustration: Fig. 139.--Nasal Horn of Iguanodon.