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Considered broadly No. 3 district has the form of a parallelogram sloping gently downwards from east to west, with its longer sides running north and south, its shorter sides east and west, and it has an area of about 200 acres. Within this area the Main-band is about 10 feet thick, and has, for the most part, an exceptionally good sandstone roof, but towards its northern end, which is not at present accessible, a certain weakness of weaker strata is said to intervene between the coal and the sandstone.

The system of working, practised here and elsewhere in the Main-band seam, is to drive two series of galleries in the coal, one series running north and south, the other east-north-east and west-southwest. The galleries are 6 yards wide ; those of the first named series are from 30 to 40 yards apart ; those of the second, from 25 to 30 yards. By this means part of the seam is gradually worked away leaving the remainder in the form of pillars surrounded by open spaces. When the workings have reached the natural or artificial boundary of a district the pillars are successfully removed in retreating backwards, and the roof, being thus deprived of support, falls in the empty space and forms what is called "goaf."

This section of the workings was ventilated by means of a current of fresh air drawn from the supply passing along the main intake. This subsidiary current or "split" of air was guided northwards along the bottom level by means of brickwork stoppings built between the coal pillars on its rise and dip sides ; then upwards in one of the east-north-east galleries, isolated in the same manner, to the points at which coal was being worked ; then southwards through the working places, and from the last of these to the main return airway.

With the exception of a large area of solid coal between 300 and 400 yards square at a distance of about 400 yards north of the main return airway, and extending from the 9-fathom fault down to within about 100 yards of the bottom level, all the coal in No. 3 district had been traversed by a network of galleries and only the pillars remained. Some of these pillars had been partly or wholly, taken out and a goaf formed in the extreme north-eastern corner of the district ; others had been taken out along the side of the 9-fathom fault and a second goaf formed. The two goaves are 200 yards apart, with several large unworked pillars intervening between them. The length of the south goaf, measured along the line of the level course, is between 400 and 500 yards, and its width on the line of dip about 60 yards at its northern end and 40 at its southern end.

The north goaf is practically inaccessible at present ; but one has no difficulty in passing along the lower sides of the pillars nearest the south goaf, or in going up to the edge of the fallen ground in the boards, or in entering some distance into the goaf itself, near Mcquillam's pillar, where the roof is not much fallen.

The seam produces a certain quantity of firedamp, which naturally rises into and occupies the goaves, which here constitute the highest parts of the workings. But having once lodged there it cannot be swept out by the mechanical force of a current of air, because it is impossible to erect and maintain an artificial barrier amongst the falls of roof ; and thus it comes to pass that the firedamp having once for all settled in the placid recesses of the goaf, remains there undisturbed except by an occasional fall of roof. From this position it can only escape by diffusing into the less contaminated mixture of gas and air lying below it, which moves in eddies in consequence of its contact with the ventilating current. The volume of firedamp thus impounded necessarily increases pari paseu with the magnitude of the goaf. This continuous increment in volume could have been entirely prevented in the present case if the two short passages which formerly existed between the workings of No. 3 district and the old workings to the rise of them had not been closed with air-tight stoppings, the one near the highest point of the north goaf was closed about a year ago, the other, 60 or 70 yards south of the south goaf, about six weeks before the explosion.

I am satisfied that if these two passages had been left open the explosion would not have occurred, because the firedamp would have drained away in them as fast as it was produced and no accumulation could have taken place in either the one goaf or the other.

My views regarding probable sequence of the events before and at the time of the explosion are thus as follows :—

So long as no pillar work had begun, there was no special difficulty in ventilating the working places. When the workings reached their natural and artificial boundaries, respectively, the two passages named above were driven through into the old workings beyond them ; currents of air passed through them ; and the ventilation of the whole district was thereby improved.

When pillar working was commenced in the north goaf the passage at that point was built up, and the process of removing the pillars was carried on backwards and downwards towards the bottom level. The firedamp having now no natural outlet accumulated in and filled the newly formed goaf ; and its lower edge came so close to the working places as to be a cause of anxiety to the management.

The workmen were then brought southwards, and had taken out pillars along the lower side of the 9-fathom fault top within say, about 90 yards of the second passage, when that passage was also blocked up. This had the immediate effect of further restricting the quantity of air entering the district.

The gas produced in the pillar workings and in the goaves had now only one means of exit, namely, downwards towards the bottom level through the airway on the north side of the large block of unworked coal previously mentioned.

Under these altered conditions firedamp accumulated in the south goaf more rapidly than before, and began occasionally to invade the working places.

I think it not improbable that on the night of the 11th of May it was standing so far below the roof in the Reeds' place that these men were afraid to work in it, and that, although there was a large quantity of top coal lying on the floor, ready to be filled, they came, or were brought out, to the point at which their bodies and all their belongings were found, either for the purpose of considering what they had better do, or, as has been suggested, to work a bench of coal off the side of a pillar so as to avoid losing a night's work. Similarly, Mcquilliam and his comrades, who were working away the southernmost pillar in the goaf close to the Reids' place had, for some reason — possibly on account of uneasiness manifested by the roof, possibly because of the proximity of the gas — abandoned the idea of filling the loose coal that lay at a higher point on the side of their pillar, and began to work off solid coal at its lowest level. The shift of men that preceded them had filled 35 wagons of that loose coal, and I saw the remainder of it still lying at the side of the pillar on the 14th inst.,* where they had left it.

Be this as it may, the firedamp was ignited at a damaged or defective safety lamp at 7.45 p.m. Judging now by my own observation of what took place in a damp mine in which I was an eye-witness of a firedamp explosion, the flame spread rapidly, but by no means with lightning-like rapidity, along the under surface of the nearly pure, and therefore inexplosive firedamp in the goaf, consuming that portion of it which was sufficiently mixed with air to burn. At this stage there was a pause of some duration. In the case which came within my own experience the pause lasted long enough to enable me and two companions to crawl back some 12 or 13 feet through a small partially obstructed passage about four feet square which constituted the only entrance to a large chamber 60 or 70 yards long by 15 feet wide, to run a short distance sideways from the direct line of the passage, to turn round when we came to the solid coal which barred further progress, and to wait for several seconds longer before a large blue flame shot out as if through the nozzle of a blow-pipe to a distance of 30 or 40 feet, or more, with a roar like thunder. Having continued for 10 or 15 seconds the flame was sucked in backwards out of sight, followed by a supply of fresh air ; then after a similar interval it shot out a second time, was again drawn back, and shot out a third time, each succeeding time more feebly than the first, and finally disappeared. Mr. Rider Haggard has accurately described the same phenomenon in "She," which appeared some years later.

I wish to draw very particular attention to this pause. It was then that the great body of inexplosive firedamp was being heated, agitated and expanded by the combustion of the comparatively thin layer of inflammable air and gas going on underneath it. It was then that Mcquilliam and his comrades, and others nearer the Dilly, having seen the first flash, fled from their working places. I can see no other feasible explanation of their absence at such a distance from them. After flowing and ebbing, the firedamp mixed with air in the process, emitted a rush of flame, which created an air-wave. The latter licked up the coal dust from the floor and mixed it with the air through which it passed. The flame of the firedamp passed directly into the fresh fuel thus prepared for it, and following closely behind the air-wave, passing forward with ever increasing force, swept through the whole district, and burst into the main engine plane at the friction gear.

It is a popular error to suppose that firedamp is an explosive substance like gunpowder or dynamite and that it will explode on the application of a flame. It cannot explode or even burn unless it is mixed with air. The mixture that explodes with the greatest violence contains about 9½ per cent. of firedamp and 90½ per cent. of air ; one containing 16 per cent. which is the upper limit, or six per cent., the lower limit, will burn quietly without explosion. No mixture containing more than 16 per cent. or less than 6 per cent. will burn at all.

Coal dust, on the other hand, is perfectly harmless so long as it lies on the floor. Like firedamp it must be mixed with air before it can burn or explode. The mixture must contain so much coal dust as to be suffocating ; and its ignition must be effected by means of a large flame, such as that of a firedamp explosion or a blasting shot.

A safety lamp may be carried into the most explosive mixture of firedamp and air without either bursting, as Mr. Blair expressed it, or being, damaged in the slightest degree. But as soon as it is perceived that the air is inflammable the person carrying the lamp should retire into purer air, as the firedamp continues to burn in the inside of the lamp and may heat it to such an extent as to crack the glass. Even this contingency need not necessarily give rise to an explosion as the flame cannot pass from the inside to the outside of a lamp except through an actual opening of a certain minimum magnitude ; but there is always the danger of part of the glass falling out and providing the opening required.

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* This refers to November. — R. A. S. R.