TUNNBLLING THBOUQH VABIOUS STRATA. 165 



square, as it is much choapor to drive a Loading of sufficient 

 dimensions tLan to have to widen afterwards. It is often 

 the case that tunnel lieadings, througli hard ground and 

 wlioro no timbering is required, are driven too small, under 

 the mistaken idea of its being economical, but it is not so, 

 as working in a cramped space, specially in rock, is always 

 disadvantageous, especially when proceeding to enlarge to 

 the full size of the tunnel; and when the advantages' of the 

 large heading, as well as the additional amount taken out 

 of the full size of the tunnel by it, are taken into account, 

 they more than balance the extra cost of driving the head- 

 ing of ample size. This, of course, must be taken to mean 

 of ample size only to leave room for proper working, as it 

 would not pay to take out the full size of the tunnel in the 

 shape of a heading, besides being a waste of time. It is 

 not always waste to expend a little more money on the 

 speed of tlio heading, as the faster the heading advances, 

 the more energy and scope is left for completing the tunnel, 

 and a slow heading always cramps the remainder of the 

 work; therefore increasing the speed of the heading-driving 

 is often money well spent, although the actual cost of the 

 heading may be enhanced. A point of considerable im- 

 portance in the economy of completing a tunnel through 

 hard ground, is to exercise care in the levels, so that little 

 or no bottoming up may be left, which is always a source 

 of groat trouble and annoyance. The author has often 

 knowrl headings of this kind driven in a careless way, not 

 from wrong levels having been used, but from the miners 

 not being properly looked after, and which generally entails 

 a lot of expense and trouble afterwards, which might easily 

 have been avoided. The same remarks refer in an equal 

 er even greater degree to keeping the heading as true as 

 possible to the centre lino. The author has often, when ho 



