SUBSTITUTIOX. 3U7 



which the ore is not known to form pseudomorphs the liypothesis of substi- 

 tution must be very carefully weighed. 



Cinnabar is reported to occur as pseudomorphs after several metallic 

 sulphides. At least one of these changes, the replacement of pyrite, appears 

 to require confirmation, but they are of no importance here, since they have 

 no bearing on the theory of the substitution of cinnabar for wall rock. 

 Cinnabar is also known as a fossilizing mineral, indicating tiuit it may 

 replace organic matter. As has been stated in the description of Sulphur 

 Bank, cinnabar is precipitated from solution by ammonia, though not at 

 high temperatures and pressures. It is possible that herein lies tlie expla- 

 nation of the fact that, while cinnabar is known to have replaced organisms, 

 the presence of carbonaceous shale or of bituminous substances in the 

 mines, wdiether of California or Europe, is not commonly of itself any indi- 

 cation of unusually rich or abundant ore. It may be, however, that such 

 substances sometimes have an appreciable effect. "If quicksilver," says 

 de Prado, "exhibits an affinity or, if you choose, a propensity for any other 

 substance, it is for carbonaceous or bituminous matter."' 



Cinnabar is also said to form pseudomorphs after two non-metallic 

 minerals, dolomite and barite. Dr. E. F. Durand is the only authority cited 

 for the statement that it replaces barite.^ On reference to his paper it 

 appears that this observer found in the Redington mine a tabular crystal 

 of cinnabar which did not seem to him referable to the rhombohedral sys- 

 tem ; and he hence inferred that it must be an example of dimorphous cin- 

 nabar or a pseudomorph of cinnabar after some other mineral, very likely 

 barite. This is a mere suggestion, and not an assertion. It was unsup- 

 ported by measurements of angles or other evidence, and barite has never 

 been found in the Redington mine. It is clearly incorrect to cite this crys- 

 tal as a case of the otherwise uidvnown pseudomorphism of cinnabar after 

 barite. 



Of the pseudomorphism of cinnabar after dolomite also only one case 

 seems to be recorded. It is said to have been reported by Blum^ in 1863 



' BuU. Soc. gdologique Frauce, 2d .series, vol. 12, 1855, p. 24. 

 sproc. Cal. Acad. Nat. Sci., vol. 4, 1872, p.211. 



' PsendomorpUosen, Appendix III, cited iu AUg. und chom. Geo]., Roth., vol. 1, 1879, p. 184. This 

 appendix is not at present accessible to me. 



