“Four squads worked at a time, each one consisting of a foreman and from 25 to 30 miners. Each squad worked six hours without interruption. This shift, apparently light, was found, on the contrary, to be very heavy, owing principally to the development of nitric gases which poisoned the air, and to the dust caused by the drills. “At first the only explosive used was military gelatine; later, dynamite-gelatine. The system of over-charging the holes was always adopted, in order to reduce the _débris_ to minute particles, easier to be transported and unloaded. The work was carried on in sections, varying from 1·80 by 1·80 metres to 2 by 2. The flat stretches of the tunnel were laid with Decauville rails. All material was carried out in cars and dumped into a hopper discharging into a large pipe. (The dump was accumulated at a point beyond the observation of the Austrians.) The average rate of progress was 5·10 metres per day.” It may be well to explain here that it was not possible to begin tunnelling on the same level at which the mine was to be exploded, but considerably more than 150 feet below that level. The tunnel, had, therefore, to be driven on a steep gradient. Another point which the report does not make clear should be borne in mind, viz., that the tunnel divided in the heart of the Castelletto, the main bore being driven on to where the mine was to be exploded, while a smaller branch--referred to below as the “Loop-holed Tunnel”--was run up to a point where favourable exit could be obtained for charging into and occupying the crater of the exploded mine. In all 507 metres of tunnel had to be driven, involving the excavation of 2,200 cubic metres of rock. The details of this work are given in the report as follows: (A) Chamber for Sullivan Compressor: Dimensions: 5 × 8 metres; average height 2·20 metres. (B) First part of gallery to second dump of material. Length 72 metres; inclination 38·70 per cent.; elevation gained 25·90 metres. (C) Second dump of material, established in order to free space for further work and reduce the length of transportation. (D) Ingersoll Group chamber. Dimensions: 4 × 6·50 metres; average height 2 metres. (E) Cut from the gallery of the second dump of material to the beginning of the ascent to the mining chamber. Length 136 metres; inclination 4·70 per cent.; elevation gained 6·40 metres. (F) Ascent to mining chamber. Length 22 metres; inclination 36·30 per cent.; elevation gained 10·75 metres. (This ascent, in order to facilitate tamping, was worked by dividing it into three sections of 1 × 1·60 metres, at nearly right angles.) (G) Mining chamber. Dimensions: 5 × 5·50 metres; average height 2·30 metres.