1918.] The N.Z. Journal of Science and Technology. 177 
Under the microscope the rock is seen to be a norite containing stout 
prisms of strongly schillerized hypersthene, with which are often intergrown 
irregular crystals of greenish-brown hornblende also strongly schilledzed. 
The other main constituent is feldspar, labradorite or even a more basic 
variety, showing broad banding between crossed nicols and moulded on the 
hypersthene. Other constituents are brown mica and iron-ores, while stout 
prisms of apatite are not uncommon. 
The chemical composition of this rock, determined by Dr. Maclaurin, 
is as follows :— 
Silica (Si0 2 ) .. .. .. .. .. 50*54 
Alumina (A1 2 0 3 ) .. .. .. .. 15*99 
Ferric oxide (Fe 2 0 3 ) .. . . . . .. 3*56 
Ferrous oxide (Feo) .. .. .. . . 7*81 
Titanium dioxide (Ti0 2 ) . . . . .. . . 1*03 
Lime (CaO) .. .. . . . . . . 10*14 
Magnesia (MgO) . . . . .. . . 6*69 
Soda (Na 2 0) .. .. .. .. .. 2*55 
Potash (K 2 0) .. .. .. .. .. 1*27 
Moisture lost at 100° C. . . . . .. . . 0*09 
Water and organic matter . . . . .. 0*59 
100*26 
A Report on a Coal-dust Explosion at Ironbridge Colliery, 
Denniston. 
By Frank Feed, M.I.M.M., Inspecting Engineer of Mines. 
On the 23rd May, 1917, at 11.20 a.m., a coal-dust explosion, fortu¬ 
nately unattended by loss of life, occurred in the Deep Creek section of 
the Ironbridge Colliery, the property of the Westport Coal Company 
(Limited). 
The Deep Creek section consists of a remnant of erosion containing 
about 10 acres of bituminous coal at an altitude exceeding 2,000 ft. above 
sea-level. The coal-seam is 14 ft. thick. The method of working is bord 
and pillar, the bords not exceeding 18 ft. in width, with an average height 
of about 9 ft. ; the dimensions of the pillars are variable. The workings 
are lighted by naked lights, no inflammable gas having been seen in this 
colliery, the numerous outcrops and proximity to the surface having assisted 
in the liberation of occluded gas. Gunpowder was used for blasting. 
From the signed evidence of the colliery officials and some of the wit¬ 
nesses of the explosion, courteously supplied to the writer by Mr. Alexander 
Marshall, local manager for the company, and formerly Government 
Inspector of Mines for the district, the following account of the explosion 
has been prepared :■— 
A bord was being driven eastward at the point marked A on the plan, 
towards a place driven to split the pillar. Between the face of the bord 
and the side of the split there was only about 4 ft. 6 in. of solid coal. In 
the bord two miners were working, D. Crawford and E. Coppersmith ; 
in the split no person was employed. Crawford drilled a shot-hole about 
3 ft. 6 in. in length in a south-east direction at the face of the bord towards 
the split, inserted three plugs (1 lb.) of compressed gunpowder in the hole, 
and tamped the same with clay under the supervision of M. Connelly, 
12 —Science. 
