TEANSACTIONS OF SECTION C. 553 



favourable as associates of gold and silver. Gold is not found in combination with 

 any metal except tellurium. Instances are found in wbich it would appear that 

 wlien the pj'rites in a gold lode has decomposed, some gold bas been dissolved by 

 the permeating waters and has again been crystallised in the cavities of the quartz, 

 in a form distinct from that in which it existed previously. It is remarkable that a 

 pyrites containing manganese is always a good matrix for gold. In some lodes there 

 is evidence of the quartz having been formed first, and the metalliferous contents 

 afterwards. Such lodes are very irregular in their yield. Carbonate of lime is a 

 rare gangue for gold, but where it does occur it is very productive. The great 

 variety of the lodes in Colombia enables the miner to acquire so many data for com- 

 parison, that he is able to distinguish the trustworthy Irom the untrustworthy lodes 

 with a certainty perhaps unknown in other countries. 



Beport on fJie pro(jress of the International Geological Map of Europe. 



See Reports, p. 241. 



