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LIGNITES, OR BITUMINIZED WOOD.

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matter, clay and sand, afterwards converted into coal, shale and sandstone, under great superincumbent pressure, possibly of the ocean.

Lignites occur abundantly in oolite, passing into coal at Carpona, and in the island Veglia, where they are excavated for the use of the Trieste steam boat. The lignite mines of Buda in Hungary are remarkable for the supply of fuel which they afford. It seems to be admitted by Brogniart that the supposed coal of the south of France is a lignite formation, occupying a higher part of the series than the last examples, and lying in the green sand deposit.

There are extensive mines in Provence, about Marseilles and Toulon, where twenty-eight beds are wrought. The principal deposit at Cologne is 30 feet thick; the locality also of the pulverulent lignite so valuable in painting. Lignites abound at Soissons, Epernay, Laon, St. Paulet, and some other places in France. To the lignite above the chalk, are supposed to belong those immense deposits found in the middle of the Alps, and those of Styria mined for fuel.

The lowest deposit of lignite found in the oolite is more akin to pit coal, than those found above the chalk and among traps. Oysters and ammonites have been found among them; and in the trap coalfield of Brora in Sutherland, there are, besides these shells, madreporites, the spines of echini, belemnites, terebratulæ, and other fragments belonging to mytili or cardium. Lignite, in some of its lowest deposits, forms regular beds of coal, sometimes of considerable thickness; and where these alternate with the shales, sandstones, and limestones of the

series, the superficial aspect is so much like that of the regular coal, that we cannot be surprised at its having been mistaken for that deposit.*

§ II. OLD RED SANDSTONE.

This sandstone forms the bottom lining of the great primitive basins in which the coal measures lie. It occurs sometimes as a breccia in large fragments, sometimes a puddingstone, sometimes a finer sandstone finally passing to an earthy mass, of porphyritic quality. The visible fragments all belong to primitive rocks, granites, mica-slates, clay slates, porphyries, quartz, &c. which resemble in nature the rocks of the neighbouring mountains. Its prevalent and characteristic dark red colour forms its

An interesting discovery has lately been made near Scarborough in Yorkshire, at Gristhorpe Bay, of a large deposit of fossil plants, presenting many varieties hitherto undescribed. They occur in the strata called coaly grit by Mr. William Smith, a pseudo-coal field below the cornbrash, being far above the geological place of the true coal measures. The plants lie in horizontal strata, those of the same species being together, as if the localities of each had been extremely limited, and as if they had been suddenly swept down by a great torrent of water. Some are very small and young; some large, and others in fructification. Several of the species are of considerable magnitude and beauty, nay even in admirable preservation. The plants are principally ferns, different from those of our coal measures, but congenerous with many now existing in tropical regions. Already 50 species have been distinguished; a prodigious variety of filices compared with those now vegetating in our climate. At Cloughton, in a somewhat similar formation, ten miles distant, there are several other kinds, totally distinct, offering a number exceeding the whole now living in the island of Great Britain. So that these northern regions, must in those ancient times, have presented as numerous and diversified a display of ferns, many of most luxuriant growth, as the wilds of Southern Africa, now do of heaths. Some of the specimens are perfectly pliant and combustible. There are also many varieties of the tree ferns, which constitute such numerous and splendid ornaments of tropical forests.-Dr. Peter Murray-Jameson's Journal, September, 1828.

MOUNTAIN LIMESTONE.

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best distinction. No important minerals appear to have been procured from this stratum; nor are organic remains usually found in it. The old red sandstone frequently forms mountains between 2 and 3 thousand feet above the level of the sea; in height yielding therefore only to the primitive and transition chains of this island, on the sides of which rocks indeed it reclines. On the borders of the forest of Dean, this formation exceeds 2000 feet in thickness, and is interposed between the transition and carboniferous limestone.

§ III. CARBONIFEROUS OR MOUNTAIN LIMESTONE.

This limestone is so named from the elevations which it attains; it is called metalliferous also; and encrinal or entrochal from its organic remains. The title of first flotz limestone, given it by the Wernerians, which signifies horizontal, is very inapplicable, since its strata are highly inclined, following the concave contour of the old red sandstone, though not quite so steep.

The texture of carboniferous limestone is usually imperfectly crystalline, and sufficiently close grained, and hard to afford marbles susceptible of a durable polish. Its prevailing colour is gray; but it has other shades,-yellow, blue, and sometimes black. Some of its beds are so pure as to contain 96 per cent. of carbonate of lime; but by foreign admixture, it passes into magnesian limestone, ferruginous limestone, bituminous limestone, and fetid limestone. Its beds are commonly very thick, extending in a continuous series many hundred feet in depth, with their interstitial seams of clay. Occasionally

it exhibits alternations of various heterogeneous rocks, particularly toadstone, grit and shale. It is a leading feature of this limestone to be full of caverns and fissures. All the considerable caverns in this island occur in this rock. Rivers flowing across its range are often suddenly engulphed, and pursue to a considerable distance a subterranean course; and the hills composed of it, exhibit often rocky dales and mural precipices. Much of the most picturesque and romantic scenery of England is formed by carboniferous limestone.

It is the great repository of the English lead ores; as those of Northumberland, Durham, York, Derbyshire, and Somersetshire. The following metallic minerals have been found in it; ores of antimoniated lead, copper, zinc, and iron.

ORGANIC REMAINS.

The animal remains preserved in the carboniferous limestone are strongly distinguished from those in the superior limestones, the oolitic and the lias, and belong in a majority of instances to entirely distinct families. These are generally common to

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ORGANIC REMAINS OF MOUNTAIN LIMESTONE. 177

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particularly encrinites and corallites exist in the greatest profusion. Some vertebræ of fish, sharks' teeth, many singular palatal tritores, and the radius of a balistes, exhibit this formation as the lowest sepulchre of vertebral animals.

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Of the crustaceous tribe, trilobites occur in this formation, as in the transition limestone; but the species seem to be distinct. Among the univalves we may enumerate the following genera :

Ammonites, nautilites, orthoceratites, euomphalus, cirrus, nerita, helix, turbo; among bivalves, modiola, mya, cardium, terebratula, spirifer, producti, a few echini, See Plate I; and among encrinites, posteriocrinites, platycrinites, cyathocrinites, actinocrinites, rhedocrinites. All the species of encrinites here are distinguished from those occurring in the lias and more recent beds, by the thinness of the ossicula forming the cup which contains the viscera. See Miller on Encrinites.

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From the profusion of these species this limestone has been often called encrinal. The coralloid remains are caryophyllea, turbinolia, astrea, favosites, tubiporus, retepora.

This limestone formation rises in England to upwards of 1000 feet above the sea level; whence

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