BY LEO A. COTTON. 515 



would proceed, with fall of temperature; and, according to the 

 observed order in the fissure-filling, quartz should be the last con- 

 stituent to crystallise; and this is found to be the case in the vughs. 



Though the order given above is typical of the mine in general, 

 it frequently happens that one of the zones of mineral is repeated 

 in the series, e.g., the arsenopyrite band in the cenire(text-fig.4). 

 Again, quartz is always more or less present throughout the 

 whole width of the vein-stuff, being intergrown with all of the 

 minerals occurring in the mine. The irregularity in deposition 

 of the metalliferous zones may be ascribed to a pulsating move- 

 ment in the solution, so that a solution which has already 

 deposited, say, a layer of zinc-blende, may, by decrease in 

 pressure, be caused to sink in the fissure, and become diffused in 

 the bulk of the solution; thus when the fissure was asain charged 

 with solution, arsenopyrite would i)robably be again deposited, 

 and the cycle of deposition be le-established. A diagram lias 

 been drawn to indicate the relative order of crystallisation(text- 

 fig.7). 



After the complete filling of the lode, further earth-movements 

 resulted in fractures trending about N.15°W., and S.15°E. These 

 have intersected both the King Conrad Lode and the Conrad 

 Lode(text-fig. 1), The faults intersecting the King Conrad are 

 due to minor movements, but that throwing the Conrad Lode is 

 on a larger scale. No deposition has taken place along any of 

 the fault-planes. 



Correlation with other Occurrences. 



Mr. Spurr, in examining the ore-deposits of Monte Cristo, 

 has tabulated some \ ery interesting observations on the order of 

 depo.sition of the ores in that district. He points out that, in 

 this mine, metasomatic changes have been so great that, except 

 in lojal crustified portions of the lode, it is difficult to make out 

 the sequence of crystallisation. In the Conrad Mine, on the 

 other hand, the lode is typically well banded, ai d the problem 

 is compai-atively easy of solution. As has been pointed out, 

 metasomatic action has not played an important part in the Conrad 

 Lode, being represented only by changes in the lode-material, and 



