THE DIAMOND PROSPECTING CORE DRILL. 379 



especially for these inacliines, with, a view to completeness and 

 economy. They are vertical, two in number, set quartering, and 

 can be driven by steam or compressed air. The hoisting appa- 

 ratus in the larger machines consists of an iron drum, wound 

 with wire-rope, and with suitable combinations of gearing for 

 hoisting the full weight of rods from any ordinary depth with- 

 out the necessity of using double blocks. For the advance or 

 " feed" of the drilling bit the single cylinder hydraulic piston 

 feed is used, except in the case of the " M " and " B " drills. 



In purchasing one of these machines it will be well to select 

 one a little larger than that just equal to the work contemplated, 

 in case the drilling should be carried deeper than was expected. 

 The location of the prospect hole should be determined by the 

 extent and general features of the land to be developed. The 

 ground should be reasonably good for hauling, and, where the 

 available supply of water is limited, it might be used over and 

 over, allowing the water as it comes from the hole to run back 

 into the tank or well from which it was pumped. The bit, when 

 it first penetrates the rock, is first set on its lowest face and 

 inner and outer edges with the small pieces of black diamond or 

 carbon. As the bit is rotated and fed forward, the diamonds chip 

 and grind away the rock in an annular hole, leaving untouched 

 in the centre a cylindrical " core." The bit passes down over 

 this " core," followed by the core shell and the core barrel. 

 The latter is a smooth-bored tube, in which the core is enclosed. 

 After drilling as many runs as will fill the core-barrel, the rods 

 are pulled up, until the top joint reaches the surface, discon- 

 nected at the joint, and the drill moves back on the frame out of 

 the way. Casing pipe is used to keep the hole clean, and to 

 prevent caving. When its use is found necessary, the hole is 

 enlarged to a suitable diameter by means of a reamer. No core 

 is made in reaming, the object simply being to enlarge the hole. 

 All the indications of the machine and gauges should be closely 

 watched, as well as the cuttings as they come to the surface, as 

 the indications shew before the rock is pulled up the thickness of 

 the strata, and the character of the rock, and they act as checks 

 which establish the accuracy of the work beyond question. 



It is undoubtedly well known that Cornwall does not enjoy 

 at the present moment that mining prosperity which so eminently 



