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Class 1 .— MINING AND MINERAL PRODUCTS.

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3. Lignite.

Lignite also occurs in Ireland , especially on tlie shoresof Lough Neagh, where it is partly used as fuel. Thevast quantity of the lignite maybe judged from a boringat Sandy Bay, described by Mr. Griffith. In 76 feet ofdepth there occurred three beds of lignite, one of 20,one of 25, and one of 15 feet thick, giving a total thick-ness of strata of fuel of 60 feet; the remaining 16 feetwere clay. Elsewhere, the beds of lignite are not somuch developed; but as the area of this tertiary basinextends over 100 square miles, the quantity of fueltherein contained may be considered of much publicinterest.

This lignite is intermediate between wood and coal, andis found on examination to present all the structure ofwood, and is of a deep brown colour. When ignited, itgives off gaseous matter, which burns brilliantly, andleaves a dense black charcoal. Specimens are found tocontain from 53*7 to 57*7 volatile matter, 30*0 to 33*6carbon, 8 to 1.6 ash.

The economic value of the lignite appears from thoseanalyses about two-thirds that of average coal. Theheat which it produces is more diffused than that fromcoal, and less intense. Indeed, in all respects as toapplication to industrial uses, the position of lignite isbetween those of coal and wood. The attempts hithertomade to render this fuel available for various economicpurposes have not been very successful.

At Bovey Tracy, in Devonshire , and at Brora, inSutherlandshire, other beds of lignite occur, and havebeen partially used; and in various oolitic beds in York-shire similar mineral fuel exists to a small extent. Noneof these, as at present worked, present any features ofconsiderable interest. Some beds of bituminous shaleat Kimmeridge, Dorsetshire , and elsewhere, have beenemployed chiefly for local purposes.

But the lignite of Ireland is far inferior, both in extentand calorific power, to that of Germany , where fuel ofthis kind exists in several places, and to a vast extent.On the banks of the Rhine, in Nassau and its vicinity,and in the east of Europe, in Silesia , and in parts ofStyria , deposits of this kind are exceedingly remarkable,and of great economic importance. Their thickness issometimes enormously great, reaching to 120 feet, andeven more, but the beds are generally detached andsmall, and more resemble drift accumulations than re-gular deposits. The value of these lignites for the ma-nufacture of iron must ultimately be very considerable,as there exist abundant supplies of iron ore in the imme-diate vicinity of the fuel, both in Austria and on theRhine, and also in Silesia .

The lignites of Germany often exhibit distinct woodystructure, and can be referred to coniferous trees. Theycontain a somewhat large per centage of ash, do notform good and compact charcoal, and will not stand theblast of a blacksmith’s forge. They are generally so wetas to require some drying before being used, and whenexposed to the air they often crack. In texture they aretough, and sometimes exhibit sufficient remains of theirorigin as to resist effectually the blow of a hammer, or,if breaking, only parting in the grain of the wood. Thechange they have undergone has* therefore, been toosmall to have given them any of the essential charactersof true coal, but they still are so far reservoirs of carbonthat we cannot doubt of their being ultimately renderedavailable.

4. Nature and Distribution of Coal.

True coal is so much altered from its original vegetablecondition as to have left scarcely any traces of its truehistory. It is generally, however, associated with sandsand clays, exhibiting numerous fragments of the ancientvegetation that obtained at the time of its formation;but these fragments are so far removed in every respectwith the existing form of vegetation, as to afford littleclue to the ancient condition of the earth in this respect.In coal all trace of true woody fibre has disappeared; thewater originally present, and so injurious in the lessaltered forms of vegetable fuel, is entirely absent, or,

if present at all, is so rather mechanically than chemically,while the water originally in the plant appears to have un-dergone decomposition, the hydrogen uniting with somepart of the carbon to form carburetted hydrogen gas, oftenexisting in the cells and between the plates of the coal,under considerable pressure, and the oxygen being almostentirely removed. The former vegetable has now becomea mineral substance, and lies in vast beds of variablethickness, and overlying each other to the extent some-times of more than a hundred in a single district; suchbeds being regularly interstratified with deposits of sandand clay, and occupying a distinct geological position,being, with only a very few exceptions, confined to rocksbelonging to the newer part of the palaeozoic series.

Between the Arctic Circle and the Tropic of Cancerrepose all the principal carboniferous formations of ourplanet. Some detached coal deposits, it is true, existabove and below those limits, but they appear, so far aswe know, to be of limited extent. Many of these south-ern coal-fields are of doubtful geological age: a feware supposed to approximate to the class of true coals,as they are commonly styled; others are decidedly ofthe brown coal and tertiary period; while the remainderbelong to various intermediate ages, or possess peculiarcharacters, which render them of doubtful geologicalorigin.

The coals of Melville Island and Byam Martin’s Island certainly a])pear to be of the true coal period. We knowthat coal exists at numerous intermediate points, fromthe 75th to the 27th degree of north latitude in America ,and also that it is worked on the Sulado and Rio Grande rivers in Mexico , for the use of the steamers.

Southward of the Tropic of Cancer, the existence ofcoal, corresponding with the European and American hard coal, is somewhat uncertain. There seems to benone on the South American continent, unless it be atAno Paser, which needs confirmation, or in the provinceof Santa Catherina, in Brazil. On the African continentwe have had vague accounts of coal in Ethiopia and atMozambique, also at Madagascar ; and quite recentlywe have had intelligence of large quantities of coal inthe newly-ceded territory above Port Natal , on theeastern side of Africa ; but we believe no geologist hasexamined those sites. In the Chinese and Burmese em-pires only brown coal appears to ,approach the tropic, buttrue coal seems to exist in the northern provinces.Southward of the Asiatic continent we are uncertain ofthe exact character of the coal deposits, such as occurabundantly at Sumatra, Java, and Borneo , and neigh-bouring islands. Coal, however, exists in these islands,and is of fair workable quality.

In New South Wales , the great coal-range on theeastern margin of that continent has sometimes been de-scribed as resembling the Newcastle coal in England,and sometimes it is described as of more ancient date.This coal differs essentially from that of any knownEuropean formation, but bears a strong resemblance tothe Burdwan coal of India .

We have not yet arrived at the period when we couldpronounce with any approach to certainty on the actualnumber of coal-basins in the world; the total numbermust, however, amount at least to from 250 to 300 prin-cipal coal-fields, and many of these are subdivided, by thedisturbed position of the strata, into subordinate basins.*These basins or coal districts are, however, grouped into acomparatively small number of districts, and even manyof these are little known, and not at all measured. Thegreater number occur in Western Europe and EasternNorth America, while Central and Southern Africa ,South America, and a large part of Asia , are totally with-out any trace of true carboniferous rocks. The remarks,therefore, that will follow, chiefly refer to the coal ofour own and adjacent countries, or of the United States and British North America .

There are various kinds of coal obtained from minesworked in the true coal-fields, which may be groupedinto bituminous coal, steam coal, and anthracite. Of

* Taylor's “Statistics of Coal,” Introduction, p. xxxvii.