396 Report S.A.A. Advancement of Science. 



diamonds fetch more in the market than those used for decorating 

 the person, and even Kimberley diamonds, since the war. have not 

 only advanced immensely in price Imt have become scarce. 



SETT IXC CROWNS. 



The steel crowns, or l)its, in which the diamonds are mounted, 

 vary in outside diameter from 2 to 6 inches, and in length from 3 to 6 

 inches. They have a female thread for attachment to the barrel in 

 which the core cut is carried, and are .set alternately on the outside 

 and inside of the cutting face, which is |" to f" in width, with six, 

 eight, ten, or twelve stones, according to the size. The insides of 

 the crowns are tapered, so that an annular hardened steel ring, 

 grooved and bevelled, placed in the larger space, more remote from 

 the cutting face, between the tapered inside of the crown and core 

 of rock cut by the diamonds, will, if the crown and core barrel be 

 lifted out by the boring rods, grip the core, break it off, and bring it 

 up. Reamers for enlarging boreholes are similar in construction to 

 the crowns, except that the reamers have a slightly wider face and 

 have guides projecting, to ensure their filling exactly the borehole 

 which is being reamed. The steel of the crowns is found tcj wear most 

 in .sandstone, and diamonds boring in that rock require frequent reset- 

 ling, for should a stone become loose and drop from its mounting, the 

 crown will rotate upon it and quickly break the rest of the diamonds. 

 The actual wear of the diamonds is considerable, and the harder the 

 rock the more wear they sustain. The loss by breakage, however, is 

 generally due to unequal density of rock, such as is met with in the 

 formations which have fine veins of quartz infiltrated in them, or are 

 of the nature of a conglomerate. All crowns and reamers are .set 

 and dismounted, at the shop for that purpose in Cape Town, by 

 skilled and experienced diamond setters, and are despatched by 

 registered post to the boring operations all over the Colony. 



COST 01- bORKS. 



The cost of boring is a most difficult matter to state. Bore- 

 holes var\' in depth, size, and hardness of the material pierced, and 

 many of them have to be lined with ircjn tubes when the ground is 

 too soft or loose to stand alone. The value, too, of the skilled fore- 

 man's services, of machinery, diamonds, tran.sport, and all the other 

 items which go to make up the cost, fluctuates considerably. And. 

 again, the conditions under which the work is undertaken greatly 

 influence the cost. The want of modern and economical machinery, 

 or a disturbed political and commercial state of the countn,", will 

 prevent the carrying out of the work in the minimum of time. Wars, 

 cattle diseases, droughts, or interrupted railway services, cause end- 

 less delays, and paralyse ever)- effort at economic organisation. 



The past five years of boring work have unfortunately embraced 

 almost every factor calculated to retard economic operations and 

 divert funds from their legitimate channel ; and it is beyond question 



