and plagiostoma; the whorled univalves, nerinoa and pleurotomaria; and, above all, the chambered shells, ammonite, nautilus,

33

1, Eryon; 2, Megacheirus; 3, Archæoniscus; 4, 5, Cyprides-natural size, and magnified.

and belemnite.

Of these testacea, the gryphæa is so abundant in the lias, that it is sometimes termed the "gryphite limestone,"

1, Gryphæa; 2, Modiola; 3, Avicula; 4, Trigonia; 5, Pholadomya; 6, Plagiostoma: 7, Nerinæa.

"nerinæan limestone." The most notable order of mollusca belonging to the period was undoubtedly the cephalapodous-that is, having their organs of motion arranged round the head, like the nautilus and cuttle-fish. Of these the ammonite (so called from its resemblance to the curved horn on the head of Jupiter Ammon) seems to have thronged the waters in many hundreds of

1, Ammonites Jason; 2, A. communis; 3, A. Bucklandi; 4, Belemnites Puzosianus; 5, 6, Belemnites; 7, Belemnoteuthis.

species, and of all sizes, from shells of half an inch to shells of three feet in diameter. Gigantic cuttle-fishes were also the congeners of the ammonite and nautilus, and have left evidences of their existence in the belemnites (belemnos, a dart), which were the internal bones of these marvellous mollusca.

122. Of the higher or Vertebrated forms of life we have many examples of placoid and ganoid fishes, of sauroid reptiles, and four or five species of marsupial mammals. Of the ichthyolites, the teeth, hybodus and acrodus, resemble those of the shark-like

cestracion now inhabiting the Australian seas; the fin-spines are often nearly a foot in length, and serrated on one or both sides; and the large enamelled scales of the lepidotus, tetragonolepis,

and others, bear testimony to the size of these estuarine and marine fishes. Of the reptiles there are several forms of tortoise and turtle (chelonia and platemys); and others seem distinctly allied to the crocodiles, gavials, monitors, and iguanidons of tropical climates, but differing widely in their structure and apparent modes of existence. One of the most frequent forms is the ichthyosaurus (ichthys, a fish, and saurus, a lizard), somewhat

Ichthyosaurus communis.

resembling the crocodile, but furnished with paddles or flippers instead of limbs. Many species have been discovered, and hundreds of individuals varying in length from four to forty feet.

132

"nerinæan limestone." The most notable orde

longing to the period was undoubtedly the cepreme year,
is, having their organs of motion arranged rounes
the nautilus and cuttle-fish. Of these the a
from its resemblance to the curved horn on
Ammon) seems to have thronged the waters i

threemoved arisations to those

contemporaneous trap effic
retains much of its original
Wand west of Session and in

ad and dismpted by granitic
as subordinate to the trappean
mauges. The physical features
unpleasing the alterations
scale producing succession of
These undulations are very
and France, where the lime
ion, compose the ridges, and
None of these ridges are
subsoil, are dry and fer-
soils of the "coombs"

clays. The arens
Hanted and parton
here it occupies a
detached punches
portions of the sys
France, where the

Turassic system."

the southern peninsula, and workable

Virginia anted as of

of the Emush white and other existing ferns new

linned to the Austrian antiment and adjoining sex Here. ex inople, swims the wegtronie, with hss gra the key to the the palates from 12 dia N▼ april s the teth neme gantic forms of raamus ies Not only 8,`nt living températule exis, and the latter abundantly, the Australian seas, yielding food to the cestracion as their t analogues dentaless tid to the de adineus fshes alled acrodi and pronmodi, k Asnare and cycadeous plants likewise dourish on the Australian continent, where marsupial quadrupeds abound, and thus appear to complete a picture of an ancient condition of the earth's surface, which has been superseded in our hemisphere by other strata, and a higher type of mammalian crganisation.”

125. Industrially, the system is by no means devoid of importance. Some of the colite sandstones, like those of Bath and Portland, form excellent building-stones, and are largely used in the metropolis; while paving-stones and tile-stones are obtained from the indurated flags of the wealden. The limestones of the lias and oolite are largely quarried for mortar; those of the former, when well prepared, furnishing an excellent hydraulic cement. Marbles of various quality are procured from the lower beds of the weald, in Sussex, and also from some of the coralline and shelly oolites, as at Whichwood Forest in Oxfordshire, whence the term “forest marble." Fuller's earth, at one time extensively used in woollen manufacture, is a product of the oolite, and alum is obtained from the lias shales of Yorkshire. Seams of coal, which are often workable, occur in the oolite, as in Yorkshire, at Brora in Sutherlandshire, at several places in Germany, near Richmond in Virginia, and Chatham in North Carolina, in India, the Indian islands, and other localities. Indeed, many foreign coal-fields are now known to be of oolitic origin, or at all events to be of Mesozoic or Secondary age, and later than the true Carboniferous era. Jet, which is only a compact variety of coal, and lignite or wood-coal, are both found in the system, though neither is of much economic value. And recently the ironstone of Cleveland in Yorkshire, which occurs in thick beds, and over a large extent of that county, has added new industrial importance to the oolite, and wealth to that district of England-the busy popula tion of northern Yorkshire and Middlesborough being the direct result of this discovery.