474 
GARFORTII : DEEP MINING. 
The conclusion arrived at by the Commission was " That the 
increase of temperature and depth was so speculative that they felt 
it better to leave the question in uncertainty, but looking to possible 
expedients which the future may elicit for further reducing the tem- 
perature, they considered it might be fairly assumed that the depth 
of at least 4,000 feet might be reached." 
In addition to the difficulties of increased temperature there is 
also the difiiculty of maintaining the roadways consequent on the 
increased weight of the superincumbent strata. If the coal when 
in situ gives support to the overlying strata, that is by a square foot 
supporting a corresponding foot, it will be nnderstood that when a 
portion of the coal is extracted, a weight over and above the natural 
one is thrown on the remaining pillars. This difficulty has, of course, 
been experienced in working shallow mines, but in deep mining the 
greater the thickness of the superincumbent stra ta necessarily the greater 
the weight and cost of maintaining the roads for the conveyance of 
material, but especially for the purposes of ventilation. Experience 
has shown that no system of working can reduce the weight of the 
superincumbent strata, and the methods which necessitate pillars of 
coal being left, even for a short time, cannot at greater depths be 
worked witli advantage. To meet this difficulty mines have been for 
many years worked on the longwall system, that is, by removing the 
coal at one operation. This system was well-known and practised in 
Scotland, the Midland Coalfields, and at certain collieries in other 
counties, many years previous to 1871. But it was not as generally 
well-known nor practised in Lancashire and Cheshire, where the 
deepest mines have been worked, as it is at the present day. 
With reference to certain mechanical and other appliances which 
will be required for raising large quanties of coal up a deep vertical 
shaft or long incline, within a given time, or passing large volumes of 
air at an increased temperature to dilute noxious gases and for the 
purpose of ventilation, or for lighting roadways and working places at 
long distances from tlie shaft, or for haulage and other purposes, I 
venture to think there will be no difficulty. Other works and 
manufactories have already some of the appliances wliich may with 
few modifications be adapted with advantage to collieries. 
