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By Electric Signalling Apparatus. — The system of signalling was by means of electric bells, arrangements being provided for cutting out the several landings as required. The principal bell cabin was midway between the grease-hole and the 3rd North Way end, but everything in it was in such a wrecked state that no deductions could be made as to whether there had been any sparking or fusing of the wires. It was stated by the management that there was no current in the signal wires from the shaft to the bell cabin at the time of the explosion. The current was on from the bell cabin into the 3rd North and North Crosscut Way. If there was any sparking in connection with the electric signalling installation, we are still met with the same difficulty as to the presence of an explosive mixture of firedamp and air in the Main Haulage road, on which a current of over 23,000 cubic feet of air per minute was passing.

Fire caused by Friction of Rollers, &c. — A careful examination was made of all roller frames on the Main Engine Plane, but there was no evidence of any charring or burning. It was suggested that a roller frame might have taken fire owing to friction caused by a roller. Such cases are known to have occurred, and the grease and dust round about bursting into flame after smouldering for a considerable time. At Auckland Park the last set travelling along the Engine Plane was that by which the back shift hewers were conveyed outbye about 1 p.m. on October 26th. About an hour afterwards some horsekeepers traversed the same road, and if there had been any smouldering it is probable they would have noticed it. In any case the smouldering or burning would have to continue until 2 a.m., a period of over 12 hours, and then, in order that the conditions necessary to produce an explosion should be provided, a fall of roof on the outbye side must have occurred in order to raise a cloud of inflammable dust. In the absence of any charring or signs of burning this theory may be regarded as very problematical.

Water-Blast. — A suggestion made by Mr. W. C. Blackett contains the elements of possibility, and should, therefore, not be lightly put on one side without the due consideration which a theory proposed by an expert of Mr. Blackett's wide experience deserves. In reviewing his theory of a water-blast, it must be remembered that one of the old goaves on the dip side of the Main Engine Plane had been the receptacle for water pumped from another portion of the Harvey Seam. This goaf may be regarded as a bottle lying on its side, and the lower portion of it being to the dip there would probably be large upper spaces lying above which remained free from water and would therefore form receptacles for gas. Owing to changes of barometrical pressure gas would occasionally be discharged, and this would pass to the rise into the more of less stagnant return and might possibly pass across it and so leak on to the Main Haulage road, where there was practically no pressure on the intake side of the stoppings. If such a thing did occur and gas made its way through a stopping on to the Main Intake Haulage road in such quantity as to form an explosive mixture, the igniting cause has still to be found as in several of the previous theories.

Spontaneous Combustion. — Spontaneous combustion may be regarded as a possible cause of the explosion, and it is quite likely that considerable heating and oxidization could take place as a result of the water which was pumped into the goaf on the low side of the Engine Plane. No peculiar odour or "gob-stink" had ever been noticed either before or after the explosion, which one would have supposed as probable on the road between the Main Engine Plane and the low side goaf in the event of a gob-fire occurring in the low side goaf.

Cases of spontaneous combustion in coal mines in the County of Durham are extremely rare, but that Durham mines are not immune from underground. fires, due to this cause, is evidenced by the following record of spontaneous combustion supplied by Mr. S. Hare, which occurred at the Ravensworth Shop Pit during his management of that Colliery in 1901. Certain winnings were being driven in the Low Main and Six Quarter Seams, which in that part of the mine were only separated by an inch of band. The six Quarter Seam was 4 feet thick, and the top portion contained several small bands and pyrites, and owing to the bad "roof stone" above and the inferior quality of the upper part of this seam, a foot of coal was left as a roof. The Low Main Seam consisted of 4½ feet of good coal. As one of the winnings 6 feet in width was known to be approaching an old water level, one front and two flank holes were kept in advance, and boring was also carried out in the other places. Two straight holes had been bored, one 9 yards long and the other 14 yards, but neither holes proved the existence of the old water level, but a hole bored near the bottom of the seam did so at 5½ yards. It was afterwards found that the water level had been driven chiefly in the floor, only about one foot of the road being in the coal. The pressure of water was from 50 to 60 lbs. per square inch, and the water was gradually run off at intervals when it could be conveniently dealt with. About six months after the holing, the water having been run off, the winning was again started, and having been driven 15 or 20 yards beyond the old level it was found that the coal on one side was very hot and a narrow crosscut was put into it for about 3 feet when it holed into an old board running parallel to the winning. In this old board only the Low Main or bottom seam had been worked, the top or Six Quarter Seam being kept up for a roof. Part of this coal had fallen, and it found that the mass was very hot and ready to break into flame. About 15 tons of this hot mass was filled up and sent to the surface. No other cases of heating were met with although the old level was crossed and re-crossed many times. The heating was no doubt due to the water from the old level acting on the pyrites in the fallen coal, assisted by the oxygen which had gained access through the boreholes.

By Explosives left in the Mine. — No shot firing took place in working the coal in the Harvey Seam, and shots were therefore only fired in connection with stonework. Apparently no shots had been fired anywhere near the seat of the explosion for a considerable time, so that it was hardly likely that any explosives or detonators were hidden away in the vicinity.

In the stenton just on the inbye side of the grease hole there were two doors, and both these were blown away from the engine plane towards the return airway. It was suggested that possibly some explosive might have been left between the doors at some time, as this space was, apparently occasionally used as a rough sort of cabin for keeping gear. A careful search, however, did not disclose anything that might suggest this as a probable cause of the explosion.