day, a description of peat called in some parts of Devonshire "Blackwood," is, when cut, dried and charred, used by the smiths in tempering edge-tools. Turf," says an Irish writer, Dr. King,* "is accounted a tolerably sweet fire; and having very impolitically destroyed our wood, and not as yet found stone coal, except in a few places, we could hardly live without some bogs; when the turf is charred, it serves to work iron, and even to make it in a bloomery or ironwork; turf charred, I reckon the sweetest and wholesomest fire that can be; fitter for a chamber, and for consumptive people, than either wood, stone coal, or charcoal." Notwithstanding this truly Irish eulogy of the national bog fuel, one of the strongest objections to the use of peat for domestic fires is the disagreeable odour it emits while burning. But in this, as in many other instances, we are reminded of the adage de gustibus nil disputandum; for Mr. Loudon, in his interesting Encyclopædia of Cottage, Farm, and Villa Architecture, mentions that, in most parts of the Highlands of Scotland, peat fuel is so abundant, and the people so attached to peat smoke, that when new houses, built with stone and lime, with chimneys to carry off the smoke, were introduced on the Marquis of Stafford's estates, many of the farmers refused to live in them; and it took years, before others could be reconciled to the clean and cold appearance which they alleged was produced by the want of smoke.

* Phil. Trans. Vol. xv. Abridgment. 1685.

CHAPTER IV.

NATURAL HISTORY OF COAL.

Nature and origin of Coal-Different opinions which have been entertained on that subject-Hypothetical queries answered-Inferences and illustrations of the vegetable origin of Coal-Chemical investigations of Mr. Hatchett-Three conditions of Fossil Fuel; submerged forests, lignites or bituminized wood, and true Coal-Description of the Bovey Coal formation-Supposed state of the atmosphere at the period when the Coal Vegetables flourished-Remarks on the prodigious supply of materials-Forests and drift wood-Have the vegetable matters forming the Coal strata been floated from a distance, or did they originally grow in situations near to those places where, in their changed condition, they are now found? Causes which may have operated in effecting the bituminization of the Coal plants-Opinions of Mr. Penn and others-Supposed peaty origin of Coal-Anthracite.

OF

F the formations or suites of strata already briefly described towards the close of Chapter II., that containing the carbonaceous deposits is the most interesting its age and composition, involve problems

which engage the researches and excite the speculations, not of the mineral geologist only, but also of persons addicted to the study of pure mineralogy and chemistry. Numerous treatises have at different times been devoted directly or incidentally to disquisitions upon the nature and origin of coal; and, as might be expected, the most conflicting and even contradictory conclusions have been come to on the subject. Mr. Hatchett,* enumerates as follows, the different opinions which have been propounded with respect to the origin of this substance-of these, Mr. Penn says, "the first three are chemical and scientific; the fourth is altogether speculative and imaginary, and pertains exclusively to the mineral geology" :

I. That pit-coal is an earth or stone chiefly of the argillaceous genus, penetrated and impregnated with bitumen. But Mr. Kirwan long ago, very justly remarked, that the insufficiency of this solution is demonstrated by Kilkenny and other coals, which are devoid of bitumen, and also that the quantity of earthy or stony matter in the most bituminous coals bears no proportion to them.

II. The most prevailing opinion is, that mineral coal is of vegetable origin: that the vegetable bodies have, subsequently to their being buried under vast strata of earth, been mineralized by some unknown process, of which sulphuric acid has probably been the principal agent, and that by means of this acid, the oils of the different species of wood have been converted into bitumen, and a coaly substance has been formed.

III. The opinion of Arduino is most singular: he

Philosophical Transactions, 1806.

VARIOUS OPINIONS AND QUERIES.

59

conceives coal to be entirely of marine formation, and to have originated from the fat and unctuous matter of the numerous tribes of animals that once inhabited the ocean.

IV. Mr. Kirwan considered coal and bitumen to have been derived from, what he designates, "the primordial chaotic fluid."

Could we imagine a person, acquainted with the methods of modern physical investigation, to hear the enquiry relative to the vegetable origin of our coal fields started for the first time, it may be supposed he would naturally think of propounding a series of questions something like the following:

1. Is coal, when subjected to chemical analysis, found to yield products analagous to those derived by similar processes from ligneous matters ?

2. Have any experiments been instituted by which the conversion of wood into matter resembling coal has been effected?

3. Do there any where exist in situ, masses of matter exhibiting on a large scale, the actual stages or progress of such a transmutation as that assumed by geologists-i. e. depositions presenting the distinct transition characteristics, comprehending undoubted woody fibre in the superior, or upper or newer beds, and of true mineral coal in the inferior or lower, or more ancient strata?

4. Do the coal strata present any organic remains or other phenomena indicative of vegetable origin?

To every one of these queries a distinct answer in the affirmative might be given; nevertheless, the enquiry developes collaterally so many anomalous phenomena, that the application of facts tending to establish a conclusion at which Mr. Hatchett, and

recent geological writers in general have arrived; namely that the theory which regards vegetable substances as the principal origin of coal, much the most probable, because it is corroborated by the greater number of geological facts, as well as by many experimental results, has by no means been unincumbered with difficulties. It has, indeed, been justly remarked, that until lately the vegetable origin of coal has, in the more perfectly fossilised varieties, been rather inferred than demonstrated. Peat, we know, from actual observation, to consist of decayed vegetables. The process is going on under our eyes: we can watch its progress, distinguish its degrees, and observe its results. The lignites of the upper deposits are so analagous to peat, and so decidedly present traces of woody tissue, that we can have no reasonable doubts respecting their origin. Bovey coal is evidently dicotyledonous wood partially altered. In the coal beds of the lower formations, however, we cease to recognise decided appearances of vegetable matter, and in several varieties the texture is so compact or crystalline, that were analogy inapplicable, they could not be considered as organic. This is more especially the case with glance coal, as also with the variety called pitch coal. The foregoing are the sentiments of Mr. Witham, who, in his work on Fossil Vegetables, has delineated beautiful sections of jet, lignites, and even the cannel coal of Lancashire, in all of which the traces of organization are decided-though some of these, as the Bovey coal for instance, where the woody character is strikingly obvious exteriorly, and in the grain viewed generally, did not present those interesting appearances under the microscope, which might have been expected.