ORIGIN AND DEVELOPMENT OF OBE-DEPOSITS. 363 



has been impregnated from the fissure or the fissure filled from 

 the country. The opposing views may be illustrated as follows : — 

 Let fig. 13, pi. IX, represent a portion of a rock mass containing 

 stanniferous silicates regularly disseminated through it. The 

 rock is permeable to a solution which is capable of decomposing 

 the silicates in question. Now we may suppose that the solution 

 circulates through the mass of the rock, and (1) merely changes 

 the silicate into oxide of tin, in situ, carrying off the silica, or 

 perhaps depositing it in the vicinity of the oxide particles. But 

 (2) if the rocks be fissured, as in fig. 14, and the circulating 

 solution is flowing towards the fissure from each side, it may 

 decompose the silicates as before into oxides, but at the same 

 time transfer some of the particles towards the fissure, so forming 

 an accumulation of tin oxide near its walls at the expense of 

 the general mass of the rock. And in proportion to the length 

 of the process, and to the extent of the mass of rock thus 

 subject to the transferring solution, may we expect will be the 

 width and richness of the enriched bands. As in the former 

 case the silica may either be deposited with the tin oxide or 

 carried farther by the issuing solution. A further development 

 of the very same process may lead to a deposition of tin oxide, 

 or of quartz, or both, with varying mutual relations, in the 

 fissure itself as a "leader." Let us speak of this hypothesis, 

 which assumes a'flow and transference from the mass of the rock 

 towards the fissure, as (x). The same phenomena of leader and 

 of enriched band may be equally well explained by another and 

 opposite hypothesis (y), which supposes a stanniferous solution 

 flowing along the fissure, which may or may not deposit ore 

 material or veinstone in the fissure itself, but which permeates 

 the rock to a certain distance on either side of the fissure, 

 depositing ore material or veinstone in that bordering belt • 

 any stanniferous particles already in the rock being thus 

 practically unaltered. I doubt not that hypothesis (y) applies 

 in some cases — where definite lodes exist — even though the 

 whole mass of country rock may have been originally impregnated 

 with ore material, but it appears to me that the former hypothesis 

 is far more able to account for such phenomena as are seen at 

 Mulberry and other similar stock-works (fig. 1 PI. viii) ; in fact 

 that the fissure when very small forms rather the exit for the 

 spent liquors, and not the entrance for the charged solutions. 



