intermixed with native sulphur. In one of the rocks associated with the gypsum formation, I discovered a fossil Patella. Though a branch of the Ecole des Mines, with able instructors from Paris, had been for some years established at Moutiers, close to the salt formations, a very erroneous opinion respecting the gypsum of the Tarentaise was maintained by the professors; namely, that the gypsum merely formed an unconformable covering over the adjacent mountains. I observed it in several parts of the valley of the Doron near Moutiers, as distinctly interstratified in the calcareous mountains, as the gypsum of Montmartre is interstratified between the tertiary formations near Paris. In one of the beds of gypsum, there was a thin stratum of carbonaceous matter, which soiled the fingers like coal smut; this is the only instance of carbonaceous matter found in gypsum, that I am acquainted with.

Transparent colourless rock-salt consists of muriat of soda, nearly in the highest state of purity; or, according to Sir H. Davy, of chlorine and sodium. It has so little water of crystallization, that it scarcely decrepitates when thrown on burning coals, in which it differs from salt prepared artificially by evaporation. Specimens of rock-salt brought from the Polish mines, are less disposed to deliquesce than those from Cheshire. The deep red colour very common to rock-salt is derived from the oxide of iron. Clay or marle commonly accompany rock-salt; it frequently lies imbedded in clay in detached masses; the clay is often much impregnated with salt, which is extracted from it by solution in water. The almost constant occurrence of sulphat of lime (gyp

S

sum) with rock-salt, is also a fact of considerable interest. It is curious to observe the two most powerful acids, the sulphuric and muriatic, so nearly associated in the same place. This fact, in a more advanced state of science, may elucidate the chemical changes which have effected the formation of these minerals.

The most natural hypothesis respecting the formation of rock-salt, at least in some situations, is that before stated, which attributes it to the gradual evaporation of lakes and pools of salt water, which remained, when the ocean retired from the present continents. This mineral by slow evaporation would be separated from the impure salts that exist in sea water; and as these salts are more deliquescent than rock-salt, they might be washed away, before the beds of rock-salt were covered with earthy strata.

The occurrence of anhydrous gypsum with rocksalt, which is also anhydrous, would, however, indicate the action of heat in the formation of these minerals; for it is scarcely possible to conceive any mode of aqueous deposition that could form anhydrous gypsum: but common gypsum might be fused by heat, and its water of crystallization expelled; it would then be converted into anhydrous gypsum. From the observations of M. Charpentier at Bex, it appears that the great beds of gypsum associated with rock-salt, are always found to be anhydrous when they are laid open to the atmosphere, but they soon absorb water, and are converted into common gypsum. The saliferous gypsum in other parts of the Alps, is also anhydrous; and if it should appear that the beds of gypsum associated with

rock-salt in other countries are anhydrous, where they have not been exposed to the action of moisture, it would add much probability to the opinion, that the consolidation of rock-salt and gypsum had been effected by heat.

Before concluding the account of the red marle and sandstone formation, it may be proper to state, that foreign geologists contend for the existence of a red sandstone over coal, which is laid conformably with the coal strata, and is a part of that formation*. If such a red sandstone, distinct from the new red sandstone, exist any where in England, it is near Oldham and Rochdale in Lancashire. The sandstone of Lancashire is coloured in Mr. Greenough's Geological Map of England, as the new red sandstone, and in Mr. Smith's Geological Map, as the old red sandstone; but I am inclined to believe, that the true position (gisement) of this sandstone in

* Le Gres, masse principale de terrain houiller, prende souvent une grande extension, en abandonnant au moins en majeure partie la houille avec l'argile schisteuse qui l'envelloppe.Daubuisson, Traité de Geognosie, tom. 2.

M. A. H. Bonnard, in his Apperçu Geognotique des Terrains, p. 144, describes the red sandstone as the upper part of the coal formation.

A. Humboldt, in his Essai Geognostique sur le Gisement des Roches, p. 199, mentions a red sandstone passing into por. phyry, as the upper part of the coal formation in Germany.

Messrs. Daubuisson and Bonnard appear to have mistaken the lowest part of the red marle and sandstone, for a portion of the regular coal strata. M. Humboldt makes a distinction between the unconformable red sandstone and the porphyritic red sandstone, which he cites as a part of the regular coal formation.

many parts of Lancashire, is not yet ascertained: its relations with the coal strata are different from those of the new red sandstone in other parts of England. -I propose to revert to this subject in a subsequent chapter.

A very remarkable discovery has been recently made, of the foot-marks of some unknown quadruped in strata of new red sandstone, at the Corn Cockle Muir, three miles from Lochmaben in Dumfriesshire. They were found 45 feet under the present surface; the strata are inclined 37 degrees. This circumstance was communicated to the author by Mr. Murray, jun. of Albemarle-street, who showed him at the same time a plaster cast, taken from a slab of stone, in which the impressions were tolerably distinct, and also part of a thin stratum of the stone itself, with indistinct impressions of a similar kind. There can scarcely be a doubt, that they were the real foot-marks of a digitated animal having short toes and claws, and the foot broad in proportion to its length. The breadth of the foot is above one inch. The part of the sandstone in Mr. Murray's possession appeared principally composed of granular fragments of reddish quartz rock and felspar, with spots of chlorite or hornblende. As remains of reptiles have been found in the zetchstein or magnesian limestone on the Continent, which is as ancient as the new red sandstone, may not this animal have been a reptile allied to the tortoise ?

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CHAPTER XII.

ON PART OF THE UPPER SECONDARY STRATA COMPRISING LIAS CLAY AND LIMESTONE, AND THE OOLITIC SERIES.

Mineral Characters of Lias Clay and Limestone.—Alum Slate. Zoological Characters of Lias.The Muschelkalk of France and Germany, the lower part of the Lias Formation, wanting in England.-Lias of the Alps.-Oolite or Roestone, the Jura Limestone of Foreign Geologists.-Mineral and Zoological Characters of Oolite or Roestone.-The lower, middle, and upper Oolites.-Oxford or Clunch Clay.Stonesfield Slate, with Organic Remains of Insects, Birds, and Land Quadrupeds.-Extent of the Oolite Formation in England; its sudden termination: Observations respecting it.-Foreign Oolites.

THE great bed of dark blueish clay, accompanying numerous thin strata of dark argillaceous limestone, called lias, is the best characterized of all the upper secondary formations in England, except chalk; and it preserves the same appearance throughout a considerable part of France; and may also be traced, but with some diversity of character, into Switzerland and Germany.

The name Lias appears to have been given to it by a provincial pronunciation of the word layers; as the lias limestone strata are generally very regular and flat, and rise in thin slabs or layers when got from the quarry. Where the lias beds are pretty