102 HARBOUR CONSTRUCTION. 



freestone quarries. I was much interested in watching hard 

 black schistose rock being quarried in this manner for the har- 

 bour works at Wick, splendid blocks of the requisite sizes 

 being thus obtained, which were as well-shaped as though much 

 mason's labour had been bestowed upon them. 



When lumps of hard rock require to be split with great 

 accuracy, holes, spaced from 4 to 12 inches apart according to 

 the nature and size of the stone, are drilled in rows with f-inch 

 to f -inch drills almost through the stone, long plugs and feathers 

 being used for bursting the stone. 



Small steam-drills, mounted upon frames on which they can 

 travel, are found very expeditious and satisfactory for this 

 work, the holes put in by them being far truer than those 

 drilled by hand. 



In granite one man drills about 15 feet of such holes in 

 10 hours ; while one of the small steam-drills will put in 80 to 

 100 feet in the same time. 



Loading Bore-holes. Before inserting the powder, the bore- 

 hole should be well cleaned out and dried. 



Vertical holes are easily charged by pouring the powder into 

 them. This is usually done through a tube and funnel, so as to 

 prevent the powder adhering to the sides of the hole. 



Horizontal holes, or those inclined upwards, are best loaded 

 by first making up the required charge into one or more 

 cartridges of convenient size, which may then be easily rammed 

 in. Horizontal holes are sometimes loaded by means of a 

 cylindrical scoop attached to the end of a rod. The edges of 

 such scoop are brought well up, so as to leave only a slit along 

 the top. When it reaches the bottom of the hole, half a turn is 

 given to it prior to its withdrawal, by which means the powder 

 is emptied out. 



When holes cannot be properly dried, it is necessary to make 

 up the powder into water-tight cartridges. Wet holes, however, 

 usually occur at or below the floor-level, in which position one 

 or other of the nitro-glycerine compounds, which are unaffected 

 by wet, may be employed with advantage. 



Tamping. I have had occasion to refer to " tamping " before, 

 and it will be understood that by it is meant the filling of the 

 bore-hole after the charge has been inserted. It is an important 

 point in quarrying, and, if improperly done, may greatly reduce 

 the effect of the charge, or lead to accident. 



