412 ME. W. GIBSON ON THE GEOLOGY OE THE GOLD-BE AEING 



composed of silvery-grey micaceous matter, and is schistose in 

 character. 



The composition of the North Beef is very similar to that of the 

 Main Reef, but the pebbles are on an average smaller, and many 

 composed of quartzite are met with. 



The South Reef has usually a larger number of black quartz- 

 pebbles, and the rock is much more compact than any of the other 

 reefs. It is most like the Main Reef Leader, and is generally the 

 richest in gold, though there are patches in the other reefs which 

 are sometimes as rich. In one or two places this reef is very con- 

 siderably narrowed, but it is never quite lost. 



The Main Reef Leader calls for little remark, except that, when 

 traced east and west from the central shaft, it is found to ' pinch 

 out' in many places, giving it the local appearance of a series of 

 lenticles. 



The predominating colour both of the reefs and of the rock 

 between them (called in the district the ' country rock') is chocolate- 

 red. Many of the harder portions, however, which are unchanged, 

 are blue or bluish-grey in colour ; and in the lower (130 feet) level 

 the whole of the rock is found to be blue, except along joints and 

 faults where water can find its way. The whole of the strata at this 

 lower level, but more particularly the conglomerates, are crowded 

 with cubical crystals and ellipsoidal particles of iron pyrites, and it 

 is clearly by the oxidation of these and the consequent iron-staining 

 that the red colour is produced. The reefs also at this lower level 

 are found to retain their relative positions, but a complete change 

 has taken place in the character of the cementing material and of 

 the rock between the reefs. The conglomerates and sandstones, 

 which on the upper level are soft and incoherent, become lower 

 down dense and hard. 



The surfaces of the adjacent rocks in contact with the conglo- 

 merates — that is, the ' foot and hanging walls,' as they are called 

 — are smooth and polished, as if the beds had been pushed over one 

 another from the south. That this movement has taken place, at 

 least partially, is made clear in the eastern half of the mine, where 

 there is a reversed fault of a few feet upthrow. The pebbles and 

 cementing-material of the conglomerates show signs of having un- 

 dergone great pressure. The pebbles, which are of a beautiful 

 milk-white colour, are completely shattered ; while the cementing- 

 material is decidedly schist-like, and is squeezed in and out and 

 around the pebbles. Much silica appears to have segregated out 

 from the rock and exists now as quartz-veins. These are not 

 numerous in the Salisbury Mine, but in the mine next to be de- 

 scribed they form a very prominent feature. 



In the eastern half of the Salisbury Mine the strata are broken 

 through by a dyke of altered igneous rock whose original composition 

 the writer has not yet been able to determine. The dyke is about 

 40 feet wide, and strikes across the beds at a very acute angle alono- 

 a line of fault which shifts the reefs horizontally for a foot or two. 

 (2) The Henry Nourse Mine is situated about 3 miles east of 



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