THE MINERAL DEPTHS 



face methods. In enterprises undertaken on a largt 

 scale, borings are frequently made in regions where 

 there are perhaps no specific surface indications. In 

 such regions a shaft may be sunk or a tunnel may be 

 dug, and the condition of the underlying strata thus 

 definitely determined. This last is, of course, a most 

 expensive method, the simpler and more usual way 

 being that of making borings to certain depths. The 

 difficulty with such borings is that rich veins may be 

 passed by the borer without detection ; or, on the other 

 hand, a small vein happening to lie in the same plane 

 as the drill may give a wrong impression as to the ex- 

 tent of the vein. 



One of the most satisfactory ways of making bor- 

 ings is by means of the diamond drill. This drill 

 is made in the form of a long metal tube, the lower 

 edge of which is made into a cutting implement by 

 black diamonds fixed in the edge of the metal. By 

 rotating this tube a ring is cut through the layers of 

 rock, the solid cylinder or core of rock remaining in 

 the hollow centre of the drill. This can be removed 

 from time to time, the nature and thickness of the 

 geological formation through which the drill is passing 

 being thus definitely determined. 



CONDITIONS TO BE CONSIDERED IN MINING 



Three great problems always confront the mine 

 operator light, power, and ventilation. Of these 

 ventilation is the most important from the workman's 

 standpoint, although the problem of light is scarcely 



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