In the above sections it will be seen, that though there is a great general resemblance between the principal members in each series, there is a considerable difference in the number and succession of the minor beds; there is also some diversity in the fossils in each series. By a comparison of both sections, it will appear, that the attempt to establish an identity of beds, or even of what are called equivalents in the minor strata of a great formation in different districts, is a useless labour, and serves only to perplex the student, without leading to any useful conclusions. Nor do I think the long lists of marine shells, in a formation decidedly marine, can be of any great use, unless such shells discover some new forms of organic life distinct from what has been before observed, or enable us to infer some change in the condition of the globe, when the inhabitants of such shells first appeared. The section of Mr. J. Phillips being a coast section has the disadvantage of not being made in the true line of dip, and that of Mr. Lonsdale was unavoidably taken in different situations where the upper and under strata were not always displayed; hence such sections can only be regarded as valuable approximations to truth in each district. In Yorkshire the Kimmeridge clay is wanting, and the oolites. are covered by the chalk formation, in the lower part of which, called the Speeton clay, some fossils of the Kimmeridge clay were discovered.

The imperfect coal formations in the Yorkshire oolites contain impressions and remains of fossil

T S

plants of the same families as those in the regular coal formation, but which are stated by M. Adolphe Brongniart to belong to different species.

The attempt has been frequently made, to identify the secondary strata of Germany with those of England. The following abridged view of the secondary strata in the north-east part of Bavaria, in Bohemia, and in Westphalia, by R.J. Murchison, Esq. taken partly from his own observations, and partly from what he believes to be the best authorities, appears to be the most satisfactory and intelligible approximation to the English series of secondary formations that has yet been made: it confirms the previous statement given by Professor Sedgwick and Mr. Murchison. The order of succession in a descending series is here given.

Chalk.

Green-sand.

Portland oolite.

Solenhoffen slate, or supposed Stonesfield slate.

Middle oolite.
Jura kalk.

Inferior oolite.

Lias.

In Hanover, clearly separated from greensand.

Divisable into upper calcareous and lower siliceous sandstone.

Oolite and coral ragg, not yet discovered in central Germany.

Between Kehlheim on the S.E., and Pappenheim on the N. W.; the quarry at Solenhoffen is worked for lithographic stone. The fossil contents are pterodactyli, insects, crustaceous animals, and tellenites, with certain plants: these fossils are similar to those found in Stonesfield slate, and occur in a similar geological position.

The beds of this formation differ much in their mineral characters in different parts of Germany, but contain many of the fossils in the English middle oolites.

The inferior oolite of Wurtemberg, Bavaria, Hanover, and Westphalia, analogous to that found on the Yorkshire coast; it rests upon lias.

Lias marl and gryphite limestone occur in the countries named in the preceding section. A formation of purple, red, and green sandstone, and marl of enormous thickness, reposing on muschel kalk, and surmounted by Upper red and yel-lias. Mr. Murchison believes that the Keu

Keuper.

low marl.

per is the true representative of the English red and green marls.

Muschel kalk, wanting in England.

Bunter sandstone.

Lower red sand

stone.

Roth-todte liegende.

More than 600 feet in thickness, contains remains of the icthyosaurus and plesiosaurus, the crocodile, and turtle: the salt mines of Wurtemberg are in this formation.

Analogous to the English lower red sandstone with magnesian limestone.

The lowest red sandstone of Professor Lowest red sand-Sedgwick, like the English sandstone: it rests on transition limestone or coal measures.

stone.

It is deserving notice, that many of the beds in the above section not only contain the same fossils as those in the English series, but also preserve the same mineral characters. Where this is the case, we can arrive at satisfactory conclusions; and such beds serve as a key to the discovery of the true nature of the beds above and below them, where the characters may be less clearly defined.

280

CHAP. XIII.

ON THE SUSSEX BEDS OR WEALDEN, CONTAINING REMAINS OF LAND PLANTS, AND AMPHIBIOUS AND FRESH-WATER ANIMALS.

Extent of the Sussex Beds. Their Geological Position and Mineral Characters. — Remarkable Organic Remains of enormous Lizards and Plants, analogous to those of Tropical Climates found in the Sussex Beds. Supposed Appearance of the Country when these Animals flourished.

stone.

Petworth LimeThe Wealden Beds

Hastings' Sand and Weald Clay. · formerly furnished the greatest Part of the Iron manufactured in England. - Mr. Mantell's Enumeration of the Species of Terrestrial and Fresh Water Fossil Remains in the Wealden Beds. Observations on the Wealden Beds, and the Change from Marine to Fresh Water Formations.

In an elementary treatise on Geology, it is desirable to present to the view of the reader, not the geology of a single country, but that of the whole globe, as far as it has been ascertained. In certain countries, particular formations occupy a considerable extent, and are of great thickness; in other countries, similar formations are often wanting altogether, or the beds are so thin as scarcely to excite notice. The secondary strata cover more than one half of England, and hence the English geologist might be suspected of bestowing upon them too great a portion of his attention; but a more accurate examination of other countries has fully proved, that many of the British strata, which were formerly believed to be of very limited extent, are spread over a great part of Europe, and preserve the same order of succession as in our own island:-a description of these strata is therefore an essential part of general geology. The formations of the magnesian limestone, the red marle, the lias, the oolites, and the chalk, have risen into geological importance within the last fifteen years; and the reproach cast upon South Britain by

our neighbours on the other side of the Tweed, namely, "that there was little or nothing in England worth the attention of a geologist," has lost all its force. The beds of sand and clay, that intervene between the upper oolites and the chalk, were, however, still more recently regarded as unworthy of particular notice; but the labours of Mr. Mantell and of Dr. Fitton have made us acquainted with facts respecting these earthy and sandy deposits, which are scarcely exceeded in interest, by any discoveries in the lower strata.

The beds which are about to be described as the Wealden, because they occur principally in the Wealds of Kent and Sussex, are supposed to rest on the upper beds of oolite in these counties: they dip under the chalk hills by which they are every where surrounded, except on the east, where they are cut off by the sea. The oolite below, and the beds of chalk and green sand above, are admitted to be marine formations, but the beds of limestone, conglomerate, sandstone, and clay, that compose the Sussex beds, or Wealden, contain almost exclusively the remains of fresh-water animals and terrestrial plants, and that over a surface exposed to observation nearly sixty miles in length, and from fifteen to twenty miles in breadth. The marine beds on which the Wealden rest, must, at a remote period, have been raised a considerable height above the ocean, and become dry land, having extensive rivers, lakes, or estuaries filled with fresh water, in which the Wealden beds were deposited. Again, at a subsequent period, the whole must have sunk deep beneath the surface of the sea, and been covered by a deposition of chalk and other marine strata, a thousand feet or more in thickness. At a more recent epoch, the chalk, with the subjacent beds of Wealden, were raised to their present elevation above the neighbouring sea. However the present quiescent state of the earth may seem opposed to the admission of such great geological changes, we are irresistibly compelled to resort to