Chap. I.

GEOLOGY.

627

The fossils of the greensand are marine ; among them is the Pecten (juinquecostatus,several forms of the Cephalopoda , as the Hamite, Scaphite, and others, which distinguishthis formation from the chalk. A specimen of a Sauriau named the Iguanodon Mantelliwas discovered at Maidstone .

Oolitic System _ Wealden formation is almost peculiar to the counties of Kent,

Sussex , and the Isle of Wight; it is a local freshwater or estuary deposit, composed ofcoloured sands and clays, with lignites, conglomerates, and calcareous masses, interspersedthroughout the sands, limestone and ironstone in the clay. It is divided into four severalgroups, viz.: —

The uppermost or weald clay is blue and stiff, with Septaria, argillaceous iron-stone,and beds of shelly limestone, called Sussex or Petworth marble (fossil Cyprides). Thesebeds of limestone are made up of a few species of the univalve called Paludina, a fresh-water snail, common in rivers and lakes; the shells are sometimes decomposed, and theircasts alone remain, the interstices being filled up with indurated marl, or calcareous con-cretions. In the coarser varieties are cavities left by the decomposition of the shells; in themore compact masses a crystalline calcareous infiltration of various colours has permeatedthe mass, and given it a beauty equal to foreign marble. There are a few bivalves trace-able in this limestone, though some blocks containing large specimens (Unio) interspersedwith univalves, and fragments of reptiles, bones, &c. of various tints of green, blue, grey,&c. have been found in Western Sussex. The Petworth and Bethersden stone or marbieare extensions of the same bed. These marbles were most extensively employed duringthe middle ages for tombstones, altars, fonts, monuments, and the decorative portions ofchurches and cathedrals. Columns of it, highly polished, are distinguishable features inthe early Pointed architecture.

Secondly. — The Hastings sand, which consists of irregular alternations of sand and sand-stone, sometimes calcareous, of a grey, yellowish, or ferruginous colour, with concretions ofironstone and layers of lignite, the sandstone often having a conglomerate form, and con-taining pebbles of quartz and jasper.

Thirdly. _The Ashburnham beds, clays, shales, bluish grey limestones and sandstones.

Fourthly. _Hie Purbeck beds, clay, sandstone, and shelly limestones, with layers of vege-

table mould, and remains of trees in a vertical position. The Purbeck is found in the deepvalleys of eastern Sussex, but emerges on the Dorsetshire coast, and from the northern browof the Isle of Portland. The Isle of Purbeck is an irregular oval, 7 miles in breadth, and12 miles in length ; on the eastern promontory the chalk is in a vertical position, andbeds of sandstone and limestone are seen underlying this displaced strata; towardsthe southern extremity of the island appears the Portland limestone. The Purbeck bedsare a sort of calcareous marble, of various thickness, and of a mottled colour; they aboundin organic remains, the chief of which is a congeries of the shell Paludina, intermixed withminute crustaceous coverings of a species of Cypris; this marble bears a high polish ; it isfiner grained than the Petworth , and was much used in the decorative portions of Salisburyand Wells Cathedrals; it has unfortunately been generally placed in a contrary positionto its true bed, which accounts for the long slender columns into which it w’as con-verted flaking oflT and crumbling away. The fossils found in the Wealden formation areexclusively of a genera either fluviatile or lacustrine, such as Melanopoca, Paludina,Neritina, Cyclas, Unio, and others ; these occur in such quantities that the surface of eachlayer of marl is sometimes entirely covered with the valves of Cyclas, and beds of limestoneare composed solely of Paludina.

The species of Bulla, that of an Oyster and Exogyra, which are met with, indicate theoccasional presence of salt water. The fishes of the Wealden belong to the genera Pvcnodusand Ilybodus, as well as a species of Lepidotus ; the general form of the latter resemblesthe carp, although of a distinct kind, and somewhat allied to the pike.

Among the vertebrated animals the reptiles are the most numerous, such as the Trio-nyx and Emys genera, found at the present day in the fresh-water of tropical regions. OfSaurians there are five genera, the Crocodile, Plesiosaurus, Megalosaurus, Iguanodon, andthe Hylaeosaurus. The Iguanodon, which was herbivorous, had its teeth formed like themodern Iguanas, found in America and the West Indies ; its entire length has been com-puted at 70 feet. No skeleton of a mammiferous quadruped has been discovered : thebirds belong to the order Grail®. Of vegetable remains there are numerous varieties, allhaving the character of tropical productions; their resemblance to the living genera ofCycas , Zamia, and Esquesata, is very great; there are specimens of Conifer® allied to theAraucaria , as well as many varieties of tropical ferns.

Upper Oolite. Portland Oolite. — This is a marine formation, or limestone, aboundingin Ammonites, Trigonia?, and other exuviae: it occurs immediately below the Purbeckbed, from which it is separated by a vegetable soil, called the dirt-bed, of from 12 to 18inches in thickness, containing a large portion of earthy lignite, wdth rounded pebbles orgravel interspersed. Trunks of trees, nearly allied to the Zamias and Cycas , are alsoburied in it, and there is every evidence that when these were growing the Portland beds

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