154 COALFIELDS AND COLLIERIES OE AUSTRALIA. 



Fig. 88. Welsh. Bord System. 



maintain. Holes have to be made in the goaf to convey air to 

 the parallel road. The holes cannot be left as the bord ad- 

 vances. since the crush would often close them up; besides, 

 though closed by brattice, the air is apt to short circuit when 

 holes are made before they are required. It is noticed that the 

 roof becomes heavy about 30 yards ahead of where the pillar- 

 ing is taking place. With the modified method (Fig. 89) a 

 pair of lour-yard headings are driven with a pillar of 24 yards 



Fig. 89. New Method. 



