MITCHELL: EXPLOSIVES USED IN MINING. 
149 
demned the use of powder, because there was a tendency to a flame, 
and, of course, a flame in mines where there was any chance of gas 
being given off, was a very dangerous element. After a very long 
and deliberate examination of the whole question, the Commission 
came to the conclusion that a quick explosive was the most desirable, 
and the explosive recommended was gelatine dynamite. 
I have the pleasure to exhibit to you the best explosive cartridges 
at present known, and the various cases in which the cartridges are 
fixed inside and surrounded by water, also the electric fuse with 
detonator attached, and the battery and appliance for firing the shots. 
The effect of the firing of the explosive is instantaneous and 
gives off" no flame. It has been said to give off a few sparks when 
fired without the protecting water cartridge, but when used in con- 
junction with the water cartridge case there is no flame given ofl", and 
consequently no risk of igniting inflamable gas. It is, therefore, a 
satisfactory substitute for gunpowder. 
ON A CONCRETION CALLED ACRESPIRE. BY H. B. STOCKS, ESQ. 
In the millstone grit formation curious concretions occur, which 
are known locally by the name of acrespire. These concretions are 
found in the bed which produces the most useful stone, and entirely 
spoil the stone where they occur, rendering it unfit either for build- 
ing or paving purposes. The acrespire itself, from its hardness and 
other properties, can only be used as road metal. 
Acrespires are generally very hard and close grained, and are 
sometimes covered by a coating of friable brown sand. The general 
colour is gTey, sometimes brown, bluish-white, and white. In size 
they vary from a few inches to many feet. They are of various 
forms, the most general being oval and oblong ; sometimes nearly 
square blocks occur. 
Planes of stratification have been noticed in one specimen, but 
in all the others examined no such planes were observed. 
