ON THE BARRIER RANGES SILVER FIELD. 185 



The more central portion of the main lode, comprising a 

 length of about one mile, has a width varying from a few feet 

 to over 200 feet. The superficially changed out-crop, which 

 was composed chiefly of hydrated manganic iron stone, with 

 quartz and feldspar, rises above the surface of the gneiss rock 

 in places to the height of 30 or 40 feet, the higher portions 

 usually corresponding to those of greatest width. From a surface 

 and underground study of the lode and its wall-rock, I have been 

 led to the conclusion that the diversities in its width are not 

 mainly due to earth movements such as the sliding of the foot- 

 wall on the hanging wall, but chiefly to the decomposition of the 

 wall rocks, and the replacement of the removed material by 

 metallic ores. The most conspicuous portion of the out-crop 

 extends from Block 12 to Block 15, a distance of about one mile, 

 terminating at either end in a bold compact bluff. From the 

 bluff end on Block 12 the lode is seen to continue south-west 

 through Block 11, Central, South, and others. But from the 

 bluff end in Block 15 no direct continuation north-east is per- 

 ceptible on the surface, the gneiss rocks, which otherwise have a 

 parallel strike with the lode, are here found curving partly round 

 the bluff, thence taking a more northerly direction until reaching 

 half-way across Block 16, after which they again take a north- 

 east course, continuing through North Broken Hill and the 

 Victoria Cross. At a distance of about 320 feet south-west from 

 Block 15 bluff (that is back along the course of the lode) a vein 

 branches off to the northward, in some parts of its extension 

 showing out-crops nearly equal in size and similar in composition 

 to those on the main lode. That this vein opens out considerably 

 below the surface is proved by the underground workings on the 

 British Blocks 15 and 16. This widening of the lode from the 

 surface downwards to depths at present worked (over 400 feet) 

 is a feature, with slight exceptions, characteristic of the whole 

 line, and is evidently due to the decomposition of the rocks on 

 either side of the vein, during its superficial alteration, the 

 soluble matter being removed and replaced by metallic ores, the 

 insoluble material making up a large portion of the gangue now 

 found distributed through the orey mass. 



Besides the main, there are three loop veins, one on the south- 

 east and two on the north-west side, which are especially 

 noteworthy on account of the valuable ore deposits they have 

 been proved to contain. The composition of these veins on the 

 surface appear to be mainly quartzo-feldspathic, with a little mica 

 and varying amounts of iron and manganese. They are, in 

 places, porous from the loss of mineral matter, otherwise their 

 surface out-crops would appear to have escaped the chemical 

 actions which have operated so largely on the main lode, excepting 



