agate veins; others with their terminations crystallized: green stalactites, CHAP. 2. very rare. Several of the other kinds are now become scarce.

The fluor spar, or, as it is here termed, blue john, is frequently confound- Fluor Spar. ed with calcareous spar, from which, however, it differs essentially. It contains an acid, the most penetrating and corrosive of any we are yet acquainted with, and which is very different from the carbonic.* This, from its peculiar properties of corroding glass and silicious substances, has been employed in France for engraving glass plates, and the specimens obtained are reported to be singularly beautiful. When moderately heated, it becomes phosphorescent; in a strong heat, it melts of itself, and emits fumes that are extremely noxious; by a certain degree of heat, its blue colour is changed into a fine red, or reddish purple; but with a greater heat, all its colours are discharged, and it becomes white. Its extreme beauty has occasioned it to be manufactured into a variety of elegant forms, such as urns, vases, columns, &c. The only mountain where it can be obtained in suf⚫ficient abundance and quality for the purposes of manufacture, is situated to the west of Castleton, between Mam Tor and the eminences that compose the Long Cliff; but even here it is less plentiful than formerly, and its price has lately been advanced to £40. per ton. The mountain itself appears like an assemblage of vast rocks of limestone, without connexion or regularity, and is full of openings or caverns of immense depth. The fluor is found in pipe veins of various directions; in caves, filled with clay and loose adventitious substances: it appears in detached masses, bearing every appearance of having been broken from the limestone, on which it seems to have been formed; for it has frequently that substance for a nucleus, around which it seems first to have crystallized, and afterwards increased by accumulation: frequently, however, the centre is hollow. Some of the pieces of fluor are a foot in thickness, and have four or five different and distinct veins, but such large pieces are very rare; in general, they are only about three or four inches thick, some having only one strong vein, while others present many, but smaller: those that display a geographical figure, like a coloured map, are most rare and valuable. The prodigious variety and singular disposition of the veins, and the sudden contrasts of the finest colours which occur in this substance, render its beauty nearly unparalleled. The colouring matter has by some been supposed to be iron: Mr. Mawe imagines it to be asphalt, containing pyrites in a decomposed state; but observes, there are many singular varieties that have not undergone any analysis. The account of the chief varieties of this substance we shall extract from that gentleman's publication.

Lime.

"Fluor, or fluate of lime, generally crystallizes in the cube and its modi- Fluate of fications; rarely in the octahedral, and still more rarely in the dodecahedral form. The chief varieties are the following:

"Water-coloured crystals of cubic fluor, studded with bright pyrites: the accumulation of crystals frequently covers the pyrites with a pleasing effect. Very large and transparent cubes of fluor, with pyrites in the in

"The fluoric acid is easily obtained by pulverising the fluor, and putting it into a leaden retort, adding its weight of any of the mineral acids. Apply a gentle heat, and the fluoric acid will appear as gas, which may be caught in a vessel of the same materials as the retort." Mineralogy of Derbyshire.

CHAP. 2. side, accompanied with blende and lead ore.

Fluor.

Stalactites

mites.

Blue fluor, of a violet colour, in perfect cubes, with cubes in the interior. Amethystine and topazine fluors: the latter of a fine yellow, with internal crystals of pyrites. Dark blue fluor, with the edges bevelled on each side. Blue fluor, with one bevelled edge, or a plane on each edge. Blue fluor, with four-sided pyramids on each face. Blue fluor, indented and perforated. Fragments of octahedral fluor. Ruby-coloured fluor, in perfect cubes, on limestone. Granulated or sandy fluor, of a rose-colour.

Compact fluor in masses, formed on limestone, or in nodules. This seems an accumulation of cube upon cube, forming prisms, the surface of which are crystallized. Some of these masses, which are seven or eight inches thick, are separated in two or three places with a very thin joint of clay, scarcely thicker than paper. This variety is composed of very fine veins, and sudden contrasts of blue. Another variety, in masses, is full of holes, containing decomposed calcareous spar, in the form of brown pearl spar. This variety is lightly veined with blue; the bottom, or part next the rock, is wholly blue, and transparent; but not so dark, nor so finely figured as the veins. Another variety, harder than the former, the ground clear white, but tinged like the lichen geographicus: this never forms veins.

"A variety, having five regular veins of fine blue: this stone is much looser in its texture; and where cut across its crystallization, it presents a beautiful honey-comb appearance: there is another variety more regularly divided into three veins. The dark blue, approaching to black, is, perhaps, of all others, the most rich and beautiful; it displays a diversity of pentagonal figures, and is bituminous. The variety which has a dark blue pervading the whole mass, is loose and friable; that of one strong blue vein is much harder, very rich, and transparent.

"Fluor in detached cubes, in the limestone, appearing a little decomposed: fluor with metallic veins: fluor decomposing: fluor of a fine green tinge; and of a blue colour, in a mass of crystallized cubes, with elastic, or indurated bitumen: fluor in compact limestone with galena, in veins and small particles, filling up interstices: fluor crystallized in cubes, upon horn-stone or petrosilex: fluor in the cavities of coralloids: fluor with barytes, commonly called tiger-stone, being opaque, and full of dirty brown spots."

Stalactites and Stalagmitest are a carbonate of lime, are found pendant and Stalag from the roofs, and accumulated on the floors of several caverns, and are of various sizes, hues and forms. Of these, different articles are manufactured by the petrifaction workers of Derby, Bakewell, Buxton, Castleton and Matlock bath. Philip Gell, Esq. of Hopton, has an elegant massive vase, thirty-eight inches across and fourteen inches high, carved from a stalagmite which was found on Hopton moor.

* It is manufactured (together with the beautiful black and other marbles of Derbyshire) into elegant chimney-pieces, vascs, candelabras, and ornaments of great variety by very ingenious machinery, worked by steam, at J. Hall's spar-works, opposite the New Inn, Derby: where visitors meet with the greatest civility, and never fail being highly gratified, by inspecting the various operations carried on in this very interesting manufactory. Very fine specimens are always to be found, amongst other Derbyshire productions and fossils, at the Museum, and other Petrifaction shops at Matlock, Derby, Buxton and Castleton.

+ See page 16.

CHAP. 2.

Coralloids.-The cone within cone coralloid is found in a bed ten inches deep, on the surface of the shell marble at Tupton, near Wingerworth; Coralloids. the cones are exceedingly distinct. Another fine specimen of the cone within cone coralloid, has been found at Blackwell; and a third, at the depth of forty-seven feet, at Aldercar, in the parish of Heanor. Coralloids, with small tubes, have been met with at Eyam, agreeing in every particular with the recent coral found in the Red Sea, named tubularia purpurea : porpites, and madrepores with round branches, have also been obtained at the same place. At Stoney Middleton, some very perfect specimens of pori fungitæ have been met with; and conia fungite have been found at Ashover; as well as very elegant screw-stones. Millepores, coral, branched, with the surface and extremity punctured as if with the point of a needle; and tubipores, a congeries of coralline tubes, paralleled or variously curved, have been procured at Middleton dale. The cornua ammonis is very abundant in the black marble of Ashford; astroites, coral, of tabular texture, with small stars on the surface, and honey-comb work withinside, is likewise procured there. At Castleton, have been found the corallina reticulata, or sea fan; plates of echini, very curiously formed, the plates pentagonal, with a small point rising in the middle; spines of echini; belemnites, cylindrical, but conical at one, and sometimes at both ends, about three inches long, and three quarters of an inch thick; anomia, bivalve, one valve gibbous, and often perforated at the base, the other plane; retepores; terrebratulæ; and ostreopectines. Gryphites, bivalve, oblong, somewhat resembling a boat, but narrow, and remarkably curved upwards at one end, the valve plane, has been met with in the red clay over the gypsum at Chellaston. Rushes, branches of yew, and a substance greatly resembling a cauliflower, have been found petrified at Matlock. A regular stratum of muscle shells has been discovered eleven yards deep at Swanwick; and muscle shells have also been found in ironstone, at Tupton, Chesterfield, and Cotmanhay; at the latter place they were obtained at the depth of eighty-four yards.

Insects.

Animals and Insects.—At Ashford, a small alligator, and various groups Animals and of flies, have been found in the black marble; and also the tail and back of a crocodile, now said to be preserved in a cabinet at Brussels. At Swanwick, a beetle in ironstone, and a butterfly, have been obtained. Vegetable Impressions.—An entire sunflower, with all the seeds per- Vegetable Impressions. fectly marked, was discovered in an iron-stone over the bed of coal at Swanwick; where likewise all the following fossils were obtained: the resemblance of a bamboo; a flower of chrysanthemum, very perfect; a flower of coltsfoot; equisetum, or horse-tail; a plant of maiden-hair; several plants of fern, very perfect, in ironstone and bind; the cone of a pine tree; a branch of a box tree; and a small branched moss: the three latter in ironstone. At Holmesfield, a resemblance of the flower of a cactus has been found. Various other vegetable impressions have been met with in the ironstone and bind, both at Newhall and Chesterfield.

CHAP. 2.

List of

Fossils.

The following FOSSILS, found in the Limestone and Ironstone of this
County, are described in Martin's Petrificata Derbiensia.

Ring-jointed Entrochite, in most of the lime. (Sacculus) Bag-like Anomite, Eyam, Monyash,

Mr. Martin has given Plates of the following in his Petrificata

Derbiensia.

CHAP. 2.

List of

Fossils.