Inspecting the Inside of the Earth 



I 



N m i n i n g 

 for coal or 



metals, opera- 

 tors must know 

 a number of 

 things about 

 their claims in 

 advance unless 

 they are out- 

 and-out gam- 

 blers. Before 



starting operations at a mine the 

 thickness, extent and richness of 

 the vein must be estimated in 

 order to determine whether the 

 mine can be worked profitably. 

 The depth of the vein from the 

 surface, the dip or angle at which 

 it lies and the nature of the ma- 

 terials that will be encountered 

 before reaching paying values, 

 are also factors of the greatest 

 importance. In a word, the mine 

 operator must have a good idea 

 of the "lay of the land" in ad- 

 vance, or he may be doomed to 

 failure from the start. 



All of these questions are eas- 

 ily answered in advance by 

 means of core drills. Think of 

 the way a corer takes out the 

 heart of an apple and you have 

 the main idea of the core drill. 

 These drills have been used for taking 

 samples out of the earth at varying 

 depths from a few yards to several thou- 

 sand feet. The speed of drilling, of 

 course, depends upon the size of the 

 core and the hardness of the rock, but 

 the average is probably between two and 



How the drill 

 samples the 

 earth through 

 which the bor- 

 ing is made 



Piles of cores from the drill. Here is a 

 record of the contents of the earth for hun- 

 dreds of feet below the surface 



four feet per hour. 

 Several typical cores 

 are illustrated. 



Figure 1 illustrates, 



in section, a core drill 



penetrating loose ma- 



t e r i a 1 composed of 



soft rock and earth. 



Here the cutting bit is 



shown with several 



sharp cutting edges, 



and the core barrel is 



about three-quarters filled with 



the different kinds of rock that 



have been penetrated. 



Figure 2 shows a core drill 

 employing a steel shot bit, which 

 type is used for cutting hai^d, 

 solid rock. The rod F extend- 

 ing to the surface of the ground 

 imparts a rotary motion to the 

 cutting tool. As the drill sinks 

 deeper and deeper, this rod is 

 extended correspondingly by 

 screwing pieces into it at the top. 

 The rod is hollow and through 

 it are fed water and very hard 

 small steel shot. The shot set- 

 tles, entering the diagonal slot 

 near the bottom of the bit which 

 feeds it beneath the rotating bit, 

 as shown at L. Here the weight 

 of the drill, combined with the 

 abrasive qualities of the shot, rapidly 

 wears away the rock and permits the 

 cutter to settle around the core. 



While the core is being made, the cut- 

 tings are washed upwards by the stream 

 of water and settle in the receptacle B, 

 which is known as a calyx. This gives 

 an additional record, in inverse order, of 

 the rock and earth penetrated, the mater- 

 ials being in pulverized form, suitable for 

 assay purposes. Figure 3 illustrates this 

 point and also shows how the core is 

 broken preparatory to extracting a piece. 

 For this purpose, pebbles are fed into the 

 drill in place of the shot. They jam 

 around the core near the bottom and 

 break it off as the drill is rotated. This 

 wedged material also holds the core in 

 place while the drill is being raised to the 

 surface. 



23^2 



