gies, and to the circumscribed ideas acquired in limited tracts of country. The views of the geologist are too grand and extensive to be shackled by microscopical differences in the composition of rocks, on which new names are so often founded, and which so far from authorizing the multiplication of sub-species, should lead to more general and enlarged views.

The work of M. Brongniart was written for the Dictionary of Natural Sciences, now publishing in Paris, which is enriched with the contributions of so many distinguished scientific men. It is divided into three parts; the first relates to the mineralogical characters, varieties, properties, &c. of lignite; the second, to its geological position; and the third, to its geographical distribution, and the circumstances therewith connected.

The term lignite is applied to no other variety of combustible mineral, than such has evidently had a vegetable origin. Under this name are included not only all the varieties of brown coal of the Germans, but likewise many other kinds of bituminous fossil coal. The distinction between fossil coal, strictly so called, and lignite, was first pointed out by M. Voigt.

The lignites are distinguished mineralogically, by a deep black colour, a brilliant lustre, a resinous fracture, which is sometimes conchoidal. Their texture is homogeneous, in which the ligneous structure is not always discernible, but in some specimens where the mineral has not lost its black colour, it is sufficiently distinct. It occasionally however passes through different shades of brown, still retaining the fibrous character. Its vegetable and ligneous origin can scarcely be mistaken, although it sometimes has quite an earthy aspect.

When exposed to the fire, all the varieties burn with a clear flame. The most compact varieties, after distillation, exhibit the ligneous structure, and those which contain no pyrites give out a pungent fetid odour, devoid of any aromatic smell; this is also the case with coal and bitumen when equally pure. In other combustibles, the pyrites occasion a sulphureous odour, different from that peculiar smell of the lignites.

After combustion, there remains a pulverulent cinder, resembling that from wood, but often more abundant and earthy, more ferruginous, and of a reddish colour, containing in some cases nearly three per cent. of potash.

VOL. II.-NO. 1.

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M. Brongniart remarks, that we have no analysis which can lead to a knowledge of the essential differences between the lignites, coal and bitumen. The three following analyses, however, of lignites from places very distant from each other, exhibit sufficiently the constituent principles.

These analyses prove the existence of an acid analogous to the pyroligneous or pyro-acetous, and confirm the supposition of Vauquelin, that this acid is formed during the combustion of the lignite. This opinion is also confirmed by the experiments of Dr. Macculloch, on the properties of the products of the distillation of wood, peat, and the lignites called jet, bovey coal, and surturbrand. All these products contain more or less pyro-acetic acid, while it is not found in the products of the distillation of bitumens; which, on the contrary, contain ammonia, &c. These analyses show that the lignites and the coals are composed of the same ultimate principles, carbon, hydrogen, &c.; but that in the products they are combined in a different manner by heat, and lead to a true mineralogical distinction between them.

The specific gravity of the true lignite, (lignite piciforme jayet,) is from 1.10 to 1.50.

The proportion of the eminently combustible part, whether it be carbon or hydrogen, to the apparent mass of the combustible, appears to be one of the distinctive characters between the lignites and the coals. The real combustible seems to be much less condensed in the first than in the second; this is not deduced from the relations of the specific gravities, which are nearly the same in the two combustibles, but from the results obtained by M. Voigt; from which it appears that one volume of lignite will give as much heat as

three volumes of pine wood, but seven volumes of the lignite of Leipsic are required to produce as much heat as one volume of coal. We know that these results are but distant approximations, and that some kinds of lignite may be chos en which will give at least as much heat as certain kinds of impure coal.

The varieties of lignite described by M. Brongniart, are the following.

1. Lignite PICIFORME, pitchcoal of Werner.

In this, the ligneous structure is sometimes apparent, but in general has disappeared.

a. Lignite piciforme commun, common brown coal, W. This variety has an unequal density, and a slaty ligneous struc

ture.

b. Lignite piciforme. Jet. The texture of this variety is compact, and it is susceptible of a good polish. It is found in beds or nodules. It never forms beds or deposits by itself, and is often met with in small masses, among beds of earthy lignite, or in trunks of black fibrous lignite. Its precise geological situation is not well known. It is found in all deposits of lignite, even in those which are above the chalk. The fine black colour of jet, and its susceptibility of being turned, cut, and well polished, renders it an object of research for ornamental purposes. But the fickleness of fashion has affected the mines and manufactories of this substance more than those of any other ornamental mineral.

After noticing the principal localities of jet, in France, Spain, Germany, England, and Russia, M. Brongniart speaks of the manufacture of jet ornaments, established at Saint Columbe in the department of Aude, in France, where it is worked into beads, earrings, crosses, &c. The manufactories at this place are in part supplied with jet from Spain. The jet is cut into small pieces nearly of the form which they are finally to retain, holes are then drilled in them, and the facets are afterwards produced by grinding the pieces on a horizontal stone, like a lapidary's wheel. The stone used for this purpose, is a coarse sandstone, and is kept constantly wet. A facet is produced by placing the piece against the circumference of the stone, where the stone is rough. The facet is polished by carrying the piece towards the centre of the stone, where it is kept smooth by means of a piece of flint carried over it from time to time with strong pressure. This process is ingenious, and the workman is ennabled to cut and polish the piece without changing his place or tool.

The jet being much softer than the stone upon which it is worked, can be shaped with great ease. A workman can cut out from fifteen hundred to four thousand pieces in a day, according to their size; a man can drill from three to six thousand holes in a day; and it is estimated, that fifteen thousand facets can be cut in a day.

One tenth part of the articles thus manufactured, are distributed through Germany, one tenth in Africa and Turkey, two tenths in France, and six tenths in Spain and the colonies. About one hundred and fifty workmen were employed in 1806, at Sainte Colombe, with a capital of about fifty-thousand francs; but in the middle of the eighteenth century, twelve thousand workmen were employed, with a capital of two hundred and fifty thousand francs.

The remaining varieties of lignite described by M. Brongniart, are

c. Lignite piciforme candelaire, cannel coal.
2. LIGNITE TERNE, Braunkohle W. moor coal.

α.

b.

C.

66

66

massive.

slaty. friable.

earthy, this includes the Cologne earth.

3. LIGNITE FIBREUX, bituminous coal of Werner.

b.

*

15

66

66

66

66

black.
cylindrical.

bacillaire, in minute fibres twisted and

interlaced.

cylindrical, in the form of a stem or compressed trunk, straight and rather longer than a goose's quill.

This variety is common, and has struck the workmen as well as naturalists, as affording one of the most certain evidences of the origin of lignites. One of the most remarkable localities is at Bruhl, near Cologne, where the number of stems and trunks is prodigious, and where are also found dicotyledons and monocotyledons.

**

66 66 66 bacillaire; there is little doubt that these are the roots or stems of trees of the palm tribe.

M. Brongniart next proceeds to point out the geological situation and connexion of the lignites, which are generally found together; some varieties predominating in certain formations, to which the others are subordinate. Viewed as a principal rock, or as forming a continuous bed, lignite is confined to one formation. As a subordinate mineral, it is

met with in masses of some size, but generally not in continuous beds, and occurs in very different formations, from the coal formation, strictly so called, to the newest formations.

Lignite is next considered as a principal rock, presenting itself in the form of a continuous bed. To this, M. Brongniart applies the term, soissonois, from one of its most important localities in France. He remarks, that lignite is considered as a formation, an assemblage of rocks and minerals, having a certain relative situation to the other rocks composing the crust of the globe. There are many of these assemblages, no one having fixed and specific characters, hence the necessity, he conceives, of adopting some term which shall designate the particular formation. The lignites of Sheppey, Cologne, Meissner, Wolfeck, &c. he continues, are precisely like those of Soissons, and under this term they are included.

The Soissons lignite belongs to the formations above the chalk, and is always beneath the inferior beds of the coarse limestone, and within the plastic clay, sand, and rolled pebbles, which are posterior to the chalk, and separate the two deposits. M. Brongniart thinks it probable there may be a second deposit of lignite in the formation above the chalk, between the gypsum and the marine formation; but this has not yet been satisfactorily proved.

The occurrence of lignite under the basalt, and in most basaltic formations, as in Hessia, Saxony, Franconia, Bohemia, in Auvergne, &c. is a remarkable fact, and tends to support the belief, that basalt is the product of the last revolutions which the earth has undergone, and induces us to regard this rock, in part crystalline, and often accompanied with rocks wholly crystalline, as posterior to those formations which were formerly called alluvial; but this does not decide the question in regard to the aqueous or igneous origin of basalt.

It cannot longer be admitted with M. Schlotheim,* that the lignites belong to the trap formation, just noticed; they must be considered as of anterior origin to this formation, and absolutely independent; for in many places where it is abundant there are no indications of a trap formation.

M. Brongniart enumerates the following as the rocks and minerals, usually associated with lignite; white and fine quartzose, and coarse ferruginous sand, siliceous pudding

*Leonhard's Taschenbuch.