Carex and grasses, with roots of Erica, and bark of birch, and probably alder-twigs abundant. Same locality as XXII.

XXIII. Very dense peat, of a blackish-brown colour. Mass compact. Vegetable structure very indistinct. Remains of Carex abundant, and roots of Erica frequent. An excellent fuel. Same locality as XXII.

XXIV. A very dense blackish-brown compact peat. Vegetable structure almost obliterated. Fracture earthy. Full of tubes of the bark of hazel, birch and alder, and occasionally scales of pine-bark, and leaves of Carex and grass. Same locality as XXII. XXV. A rather dense reddish-brown peat. Structure very indistinct. Carex leaves altered, and occasionally a few fragments of twigs and roots. Same locality as XXII.

XXVI. Rather compact and moderately dense peat, of a dark reddish-brown colour. Structure of moss almost obliterated. Abundance of leaves, stalks and roots of grasses, Carex, &c. Same locality as XXII.

XXVII.-Dense jet-black peat. Structure of moss completely destroyed. Fracture earthy, tending to conchoidal, assuming resinous lustre when rubbed. Abundance of remains of Carex leaves, and a very few fragments of bark, apparently of hazel. Same locality as XXII.

Density of Peat.-The weight of peat depends upon its state of dryness, and its age. Karmarsh gives the following relative weights for different kinds of Hanoverian peat: 1. Light-coloured, young grass peat, nearly unchanged moss, 0.113 to 0.263. 2. Young brown and black peat, an earthy matrix intersected with roots, 0.240 to 0.600. 3. Old earthy peat without any fibrous texture, 0.564 to 0.902. 4. Old peat, pitch peat, 0.639 to 1.039. Moulded peat from Griesheim (near Darmstadt), of good quality, has been found to weigh 0.706, so that 1 cubic foot would weigh on an average 22 lbs. and 100 bricks (at 56 cubic inches), 123.5 lbs. These leave after incineration a mass of ash, which although less in bulk, retains the form of the brick, and is very considerable in quantity.

Sir R. Kane estimates the specific gravity of light surface-peat at about 0.400, and from this it increases, with the compactness of

* 1000 pieces of Griesheim Peat are calculated at 74300 c. f. and weigh 1170 lbs.

the substance, to nearly the density of coal. A cubic yard weighs, packed closely in sods, about 900 lbs. The densest turf will weigh as much as 1,100 lbs. per cubic yard, while the lightest may not weigh more than 500 lbs. Compared with coal in fragments as employed in the furnace, peat is about as dense. A cubic yard of coal averaging about 13 cwt.

The maximum specific gravity of peat from the series of 27 specimens of all kinds and characters from the great bogs in the centre of Ireland, as given at p. 22, by Sir R. Kane and Dr. Sullivan* to be 1.058, and the minimum 0.235; the greater number of specimens being however below 0.6.† The quantity of water contained in these specimens, after being dried in the air, ranged between 10.446 per cent in a specimen taken from the middle layer of a bog, and 33.270 per cent in a very dense compact specimen, in which vegetable structure was very indistinct. The mean quantity in the 27 specimens was 21.6.

A cubic foot of the earthy peat examined by Karmarsh gave nearly 3 lbs. of ash; a quantity which must be very prejudicial in many of its applications; partly from the dust which it makes and the space it occupies; and partly by its chemical action in smelting processes, destroying the bars of grates, besides decreasing, of course, the quantity of combustible matter.

The conditions under which peat is produced should have a tendency to increase its amount of carbon above that contained in woody fibre. Regnault and Mulder have both examined the elementary composition of different varieties of peat; the following are their results, after deducting the amount of ash stated in the previous table:

*"Report on the Nature and Products of the Process of the Destructive Distillation of Peat, considered especially with reference to its Employment as a Branch of Manufacturing Industry." London, 1851.

+ For details of these, see Table, page 22.

In a fire, which converted 320 lbs. of water into steam in 9 hours, 240 lbs. of peat were consumed. The ash of this, calculated at 20 per cent, would leave 48 lbs. daily on the hearth, and amount in the year to 175 cwt., the removal of which would be attended with much expense and trouble.

The last column includes the very small quantity of nitrogen in peat, which is recognised by the ammoniacal vapours that it produces on heating.

It would thus appear that peat differs essentially from wood in elementary composition. The former may be viewed as consisting of carbon and water in equal proportions by weight, while in the latter, the entire amount of oxygen being supposed in combination with hydrogen to form water, we have the following relative proportions in 100 parts:

or an excess of 10 per cent carbon and 2 per cent hydrogen over that contained in dried wood, while the amount of water is reduced 12 per cent.

The following analyses of specimens of Irish peat have recently been made, showing also the amount of nitrogen which they contain. The ash was deducted in calculating these results so as to exhibit the actual composition of the organic matter.

The following may also be added to the list; in these the ash is

not deducted.

Ochta, in Eastern Russia.

39 084 3.788

51.088

Woskres6.04 sensky.

Peat, 44ft. from surface, Tuam, Ireland 57.207 5.655 28.949 3.067 5.122

Ronalds.

These results confirm generally the above remarks. It appears from the table of ash analyses, that the amount of sulphate of lime and phosphoric acid does not depend upon the position occupied by the peat in the bog, but rather upon local circumstances; that during the formation of peat the greater part of the alkali and phosphoric acid originally contained in the plants has been removed; and that the amount of silica is very small, especially in the fibrous varieties.

The proportions of carbon and hydrogen contained in different specimens of peat do not vary much, although the lower layers generally contain a little more carbon than those near the surface.

FOSSIL FUEL, OR COAL.

The steady and gradual operations of nature, at the present day, supply certain districts with a stock of fuel of no mean quality, by the constant interment of the lower kinds of vegetation in the manner already described; but in the earlier periods of the earth's history far more extensive stores of invaluable combustibles were laid up for the future use of mankind.

The most valuable of all the species of fuel is coal, and its discovery and application have been attended with increased prosperity in all those countries which are so fortunate as to possess it.

Coal is a dark-brown or black mineral, of no great degree of hardness, varying from 1.2 to 1.8 in specific gravity, which burns with a more or less brilliant flame and much smoke when ignited, and occurs in horizontal or more or less inclined layers, alternating with clay, and frequently with ironstone, chiefly in the geological formation which, from this circumstance, has been named the Carboniferous, and which takes position in the series of sedimentary deposits between the lower Silurian or primary fossiliferous formations on the one hand, and the New red sandstone on the other. Anthracite, the oldest species of coal, is also found in the most recent members of the transition formations; and brown coal, the youngest variety, occurs in the chalk.

There appears no reason to doubt the vegetable origin of coal. The gradual metamorphosis of woody fibre into coal can be traced chemically, step by step, through the various stages; upright fossil trees, with their roots resting in scams of coal, testify to their growth upon the site in which they remain carbonized, while

modern transformations of forests into peat-bogs, in which the trees remain erect, afford the strongest analogical evidence of the manner in which many of the ancient coal-fields may have been produced. Botanists who have paid particular attention to the fossil flora of these deposits are generally agreed in ascribing them to the accumulation and gradual decomposition of ferns, some of which were arborescent, and to vegetable forms belonging to Calamites, Lepidodendra, Sigillariæ and Stigmariæ; palms, though rare, are sometimes found; and altogether there have been found not less than from 200 to 300 species of plants.

The character and habits of these plants would indicate that a very different temperature and climate, and indeed an altogether different distribution of land and sea must have existed at the time of their growth and subsequent interment. They belong to a vegetation which is known especially to flourish in an extremely moist, warm and equable climate, with the absence of any severe cold, under circumstances and meteorological conditions, therefore, which are very different from those which characterise the coal districts of the present day. A tropical climate was at one time considered essential to the growth of these vegetable forms, and a very large excess of carbonic acid in the atmosphere above that contained at this present time has been assumed in explanation of their gigantic development. Although closely allied to tropical plants, those of the coal formation are still so distinct, that the former assumption does not appear necessary, indeed the flora of the southern coasts of New Zealand, situated in the 46th degree of latitude, is stated to bear the strongest resemblance to that of the coal formations.

From considerations of this kind it has been reasonably inferred that, at the time of the carbonaceous deposits, the northern hemisphere was pervaded by a great ocean interspersed with numerous islands of small dimensions, bearing insular or submarine volcanoes, a combination of geographical circumstances not unfavourable to the growth of a flora like that from which these deposits have been formed. Alternate elevations of sea and land, islands springing up by volcanic agency from the bottom of the ocean, might cause the waters to overflow and submerge the less elevated lands, and bury with them the forests and vegetation under layers of mud and sand. A series of such alternate changes can readily be conceived to account for the various coal deposits.

By some it has been supposed that the coal-fields resulted