164 



TUNNELLINO TriROUOTt VAKTOUS STUATA. 



framo, tho diamonds being sot round tlio head of a Lollow 

 steel tube, which is revolved by the oscillating engine, and 

 thus cuts its way by sheer friction into the rock, the core 

 of which passes through tho hollow tube, coming out at the 

 end in a complete state, thus forming a perfect geological 

 section of the ground passed through, which is, of course, 

 of immense advantage in trial-boring for Artesian wells, 

 or similar purposes ; and it has no doubt done splendid work 

 in such cases, but is not adapted for heading driving. For 

 driving the heading referred to, a pair of drills were fixed 

 in the manner referred to on an iron trolly framo, and when 

 a suflRcient number of holes wore driven, the trolly was 

 run back on the ordinary rails of tho dirt wagons, out of the 

 way, until the holes were fired, when it would bo again 

 run into place for drilling. Owing to the amount of com- 

 plicated machinery, it was always necessary to have a 

 skilled fitter as foreman over the drilling ; and the cumber- 

 some machinery was nearly always in tho hands of fitters, 

 which soon rubs the gilt off of the speed whilst actually at 

 work. It is not intended to enter into any description of 

 tho different kinds of air drills, of which the name is 

 legion, although differing little in principle, and many im- 

 provements in which have been made since the diamond 

 drill first came out ; but the author thought that the fore- 

 going brief description would not be out of place,' as it is 

 not often met with in heading driving. The work done 

 in the tunnel referred to was largely through the Pennant 

 rock, and that of the liardest of its kind, although a con- 

 siderable portion lay through a hard kind of what was 

 called Clift, 18 yards per week being often driven tlirough 

 it, and 16 yards through tlie hard Pennant. A heading 

 through hard ground should be of ample size, within 

 reasonable limits, say not less then seven or eight feet 



