102 DIAMOND DIGGING IN SOFTH AFEICA. 



of the diamond, but considers the production of these precious-, 

 stones is not due to any rock more recent than greenstone. Elabo- 

 rate analyses have been made of the " blue " ground which has 

 proved of such wonderful value, but its precise nature still seems 

 doubtful. It is described as a hydrous magnesian conglomerate 

 with silica as a base. Thin veins of calc spar are of frequent 

 occurrence, and vaalite, mica, iron pyrites, and hornblende are found 

 disseminated through the diamond bearing rock, besides fragments 

 and masses of shale, sandstone, and boulders of dolerife. The 

 generally accepted theory is that the "blue" has filled the 

 crater or funael of an extinct volcano, which now forms the mine, 

 and that it has been upheaved from a vast depth, the diamonds, 

 themselves being of earlier date than the upheaval. Coal has been, 

 found in the immediate neighbourhood of the Kimberley mine, and. 

 remains of plants and of extinct reptiles are frequently to be met 

 with in the deposits of shale. 



The area of the mine originally enclosed within. the surrounding- 

 rock was about 11 acres, but as this reef has been removed, a 

 course necessitated by the increased depth of the workings, the 

 surface area has been extended to about 30 acres. The greatest 

 depth to which the surface working of the mine has extended is- 

 450ft., but underground excavation has had to be resorted to, 

 owing to the continual slipping of the loose slate or reef. In the 

 year 1883, the whole of the diamondiferous ground was covered in 

 this macner to a depth, in parts, of over 100ft., and it was estimated, 

 that the cost of clearing the mine would be, at least, £2,000,000. 

 Up to this time, over £1,500,000 had been spent in connectioa 

 with this difficulty, and several successive contractors had failed in 

 their efforts to cope with it, and as now the Banks refused further 

 assistance to the Mining Board, it was predicted that the mine 

 was ruined. The result was a crisis on the fields, which coupled 

 with a great fall in the price of diamonds, was most disastrous for 

 speculators. 



Two methods of underground mining have beea adopted, in one 

 case shafts are sunk from the surface, at some distance from the 

 margin of the mine, and tunnels driven through the hard basaltic 

 rock, which is found at a depth of 250ft. to 300ft., into the 

 " blue ground," The " Jones' system " as the alternative method 

 is called, after its inventor, is to sink shafts on the coffer dam 

 principle through the loose reef to the " blue," after which they 

 could easily be extended and the ground excavated. This system, 

 however, seems to have had but a brief period of success, as con- 

 tinual reef movements wreck the shafts, and destroy all means of 

 access to the valuable solid rock. It may be surmised then that the 

 prestige of Kimberley as the most wealthy diamond mine in the 

 world is, for a time at least, eclipsed, as the yield from De Beers 

 has exceeded the amount there raised for the last three or four 

 years. In the days of its greatest prosperity the Kimberley mine 

 contained 420 claims, each of 31ft. square, and 600,000 loads of 

 blue ground were annually raised to the surface and put through 

 the washing machinery ; a load being equal to 16 cubic feet. The 

 value of the mine was estimated at £5,000,000. It is difficult for 

 anyone who has not had an opportunity cf seeing this wonderful 

 excavation to form an idea of the immense amount of work which:. 

 has been done in a few years' time. As its name of Colesberg. 



