nites and Nautilites. It is probable that the animals that had straight chambered shells possessed greater facility of rising to the surface than the spiral ones, and accordingly we find them chiefly in the oldest and lowest formations. The animals of this class having heads and various senses seem to rank high in the scale of sentient organic beings; but they are not numerous, till we rise in the secondary strata, above the coal formation.

Very few spiral unchambered shells occur in the transition rocks*; for these animals crawl on their bellies like the snail, and do not seem fitted to live in deep water, unless, like the Helix Janthina, which nearly resembles the snail and lives in the Southern Ocean, they had little appendages like bladders, which enabled them to rise to the surface. Univaive unchambered spiral shells, become numerous in the upper strata, probably from the circumstance that these strata were deposited under shallower seas.

With respect to that class of the testaceous Mollusca which did not enjoy the privilege of having heads and eyes, their motives for travelling, whether for pleasure or necessity, must have been few indeed; and they may be supposed to enjoy life as well in the deepest recesses of the ocean, as nearer its surface. The tenants of bivalve shells, called by Cuvier, Acephalest, have, however, a power of locomotion which they effect, some by thrusting out a membrane called a foot, and with it they also attach themselves to rocks or other bodies, by a number of filaments called the Byssus, which they can remove at pleasure: others have two tubes, with which they force out water with considerable violence, and impel themselves in an opposite direction; and others again, by a strong muscular action in opening and shutting their shells, can jump twelve inches at one leap.

All these modes of motion, however, though sufficient for the wants of the animal, are very limited in their operation, and are equally adapted for animals in deep or shallow seas, in rivers or lakes: accordingly, we find numerous testaceous Mollusca of this class, not only in the transition, the secondary, and the tertiary strata but at various depths in our present seas and lakes.

* All unchambered spirals shells were occupied by animals which had an organ of motion placed under the body, as in snails: they had heads, and are called by Cuvier, Gasteropodes.

+ Acephales-having no heads.

CHAPTER XI.

TABULAR ARRANGEMENT OF SECONDARY STRATA.-RED SANDSTONE. MAGNESIAN LIMESTONE.-ROCK SALT AND GYPSUM.

Relative Geological Position of the Secondary Class of Rocks.-Their Mineral and Zoological Characters-Tabular Arrangement.-New Red Sandstone and Red Marl-Upper, Middle, and Lower Beds, formed chiefly of the Fragments of more ancient Rocks, broken by some great Convulsion.-Lowest Red Sandstone, or Rothe-todte-Liegende of the German Geologists.-Separated from the Middle Beds, by Beds of Magnesian Limestone.-Middle and Upper Beds of Red Sandstone and Marl; their Accordance with those of France and Germany-Muschel-Kalk wanting in England, but probably exists in Ireland, as the Lily Encrinite has recently been discovered there.-Magnesian Limestone of the Northern Counties.-English Red Marl and Sandstone formed of more ancient Rocks, particularly of Porphyry and Trap.-Gypsum accompanying Rock Salt originally Anhydrous.-Rock Salt Deposits, in different Formations.

SECONDARY rock formations, comprise all the regular strata that cover the transition rocks and coal measures, and terminate with chalk. Their mineral characters may be briefly described, as they occur in England, France, and part of Germany, They consist of vast depositions of sandstone and conglomerate beds, and of numerous calcareous beds, separated by beds of clay and sand. The limestones are less crystalline, and more soft and earthy, than transition or mountain limestone. They abound in remains of testaceous animals, which are chiefly marine shells; but remains of fresh-water animals occur in some of the secondary beds; and parts of fossil terrestrial vegetables are also sometimes found, proving the existence of dry land, at the period when the strata were deposited. Secondary strata cover a large portion of the habitable globe, and are the immediate sub-soil of the most fertile districts in England, and of various parts of Europe. No beds of good mineral coal are found in any part of the secondary series of strata, above the regular coal measures in England; but some beds of imperfect coal, and wood coal, occur in the secondary formations: and this is also the case in similar formations on the Continent. Neither metallic veins nor metallic beds deserving notice (except of iron ores) occur in this class of rocks; nor do they afford any of the rare species of crystallized minerals. Rock-salt and gypsum are the most valuable minerals found in the secondary strata; and it is from them that all the important salt springs issue. Some of the rocks in this class yield useful materials for architecture; but the stone is, generally, soft and perishable. To the rocks of this class, Werner gave the name of floetz or flat rocks, because, in the northern parts of Europe, they are generally arranged in nearly horizontal strata; but, this character is altogether inapplicable to the upper secondary strata in the outer ranges of the Alps, and in the Jura chain, where they may be observed, bent in every possible direction, and sometimes nearly vertical. In these

mountain ranges, the mineral characters of the upper secondary limestones also frequently undergo a considerable change, and become indurated and crystalline, like transition limestones.

It has been stated in the preceding chapters, that the coal strata, which are interposed between the transition rocks and the secondary strata, contain, almost exclusively, the organic remains of terrestrial and lacustrine or marsh plants, while the fossils in the lower or transition class, belong, almost exclusively, to marine animals. Another great change appears to have taken place in the condition of our planet, after the deposition of the coal strata, for the upper secondary strata contain, principally, the remains of marine animals. It is in the strata belonging to this class, that the bones and entire skeletons of enormous reptiles are first discovered. It is, however, truly remarkable, that throughout the whole series of the upper secondary strata, no bones of mammiferous land quadrupeds have yet been found; the strata at Stonesfield alone present a solitary exception.

In England, the order of succession of the upper secondary rocks may be more distinctly ascertained, than in any other country that has yet been examined. I shall therefore describe them as they occur in our own country, with references to foreign localities, where the same beds or formations are well identified with the English strata. Geologists on the Continent, and particularly in France, had, till very recently, no accurate knowledge respecting several of these formations; and their classifications of them were vague and contradictory. More attention, however, has, very lately, been directed to this part of the geology of France; and the clear accounts which have been published, by M. Elie de Beaumont in particular, of some of these formations, remove much of the obscurity which prevailed respecting them, and prove, in a satisfactory manner, the great similarity which may be observed, in the secondary formations of England and France.

In the following tabular arrangement of the secondary formations, above the transition and coal formations, I have not thought it expedient to introduce all the minor subordinate beds in each formation: those which possess any geological importance will be subsequently noticed. It may be frequently observed, that particular beds which occur in one part of a formation, and are considerably developed, cannot be traced even into an adjacent district, or they vary so much in thickness and mineral characters, as scarcely to be recognized. If we take an extensive formation, like the oolites, as an example, it is not possible to assign any one part of the range, as affording a correct type of all the series in distant or even in neighboring parts of the range, though we may trace a general resemblance in all the principal beds; and this I hold to be amply sufficient for every valuable purpose in geology.*

Those who know into how many mistakes even eminent geologists have fallen, respecting the formations in their own immediate vicinity, by attempting to

SECONDARY FORMATIONS,

above the transition and regular coal formations, and terminating with chalk.

1. RED SANDSTONE AND MARL WITH MAGNESIAN LIMESTONE.

a Lower beds of new red sand

stone.

b Magnesian limestone.

e Upper red sandstone.
(Muschel-kalk wanting in Eng-
land.)

d Red marl with fibrous gypsum.

a Grès

ancien et rothe

rouge todte-liegende.

b Zechstein et rauchwacke.
c Grès bigarré et grès des Vos-
ges, muschel-kalk.

d Keuper, marnes irrisées.

2. LIAS LIMESTONE AND LIAS CLAY.

a White lias and micaceous sand

stone.

b Blue lias with marlstone.

e Lias clay and shale.

Calcaires à gryphites.

3. OOLITE LIMESTONE AND BEDS OF CLAY AND SANDSTONE.

a Inferior and Bath oolites with

sandstone, Oxford or clunch

Calcaires oolitiques, and sometimes calcaires de Jura, and also calcaire Alpin.

introduce numerous subdivisions of strata, and to identify them with those in other situations, will be ready to acknowledge that such labours are too micrological, and that by endeavouring to mark divisions, where Nature has not established them, we lose our time, and introduce needless perplexity into the science. A reference to the two sections of the oolite formation, given at the end of the next chapter, will serve to evince the truth of the above remarks.

4. Lias clay and lias limestone.

5. Oolite formation, and beds of clay.