CHAPTER VI. 



QUARRYING. 



Selection of quarry site Overburden Drainage Arrangement of quarries Height 

 of working face " Strike " and " dip " of strata Small-hole blasting Weight 

 of charges Mine-blasting Line of least resistance Cranes, etc. Steam and 

 hand drilling Consumption of steel Forms of drills Explosives Seam- 

 firing Cutting stone by means of "plugs" and "feathers" Charging bore- 

 holes Tamping Firing by electricity Lightning fuse Safety fuse. 



THE manner in which quarrying is conducted is so important 

 a feature in the execution of sea-works, and may so materially 

 affect their cost, that, although the subject may be considered 

 as scarcely coming within the range of this work, I hope any 

 inconsistency there may be in introducing it here will be over- 

 looked. 



I do not propose to describe quarrying generally, but merely 

 wish to direct attention to such points as, I hope, may be of 

 use to the young harbour-engineer. 



The mode of quarrying stone for monumental or architectural 

 purposes is, to a great extent, governed by conditions which do 

 not affect sea-works, and need not therefore be referred to. 



Selection of Site. After having estimated the quantity of 

 stone required for any work, due allowance having been made 

 for waste, possible alterations in, or extensions of the proposed 

 works, and so forth, the area of land to be taken for quarry 

 purposes can be determined, the intended height of working 

 face, having reference to convenience of approach and contours 

 of the ground, having, as a matter of course, been duly con- 

 sidered. 



A sufficient number of trial pits should be sunk over the 

 surface of the contemplated quarry site, to furnish an accurate 

 knowledge of the ground. Some of these may, with advantage, 

 be carried down into the rock, with the view of ascertaining 



