18 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



irregular networks of veins, or stockworks, are also found. The limestone 

 forming the immediate walls of the layers differs from that which is more 

 remote from the deposits, the rock at the contact tending to assume a 

 blackish color and a compact granular structure. The deposits are ordi- 

 narily separated from the country rock by a deposit of gypsum.^ The 

 chief ore is cinnabar, often hepatic and sometimes accompanied by the 

 seleno-sulphide guadalcazarite, first described by Mr. del Castillo from this 

 locality. Calcite and fluorspar are the gangue minerals. Native sulphur 

 occurs with the ore in the principal vein of the district, the Trinidad. This 

 appears to me to suggest the recency of the deposit and its deposition from 

 hot sulphur springs; for most native sulphur is certainly formed by the 

 decomposition of hydrogen sulphide in contact with air. Mr. Ramirez sup- 

 poses the sulphur formed by sublimation; but I do not find in his descrip- 

 tion any evidence of the former prevalence of very high temperatures, and 

 the presence of calcite and fluorspar indicates deposition from solutions. 



The deposits of Huitzuco, about fifty miles north of Tixtla, in the 

 State of Guerrero, were discovered in March, 1874. The geology and the 

 deposits of mercury, silver, lead, and other metals of this state have been 

 described by Mr. T. L. Laguerenne.' Granite seems to underlie the coun- 

 try. Upon it rest metamorphic rocks, including serpentine and eruptive 

 masses. In the neighborhood of Huitzuco the rocks are metamorphic slates 

 and limestones Avhich have been much disturbed. The cinnabar deposits 

 are mainly pockets of various dimensions and layers, but veins also exist. 

 The deposit of Tepozonalco is a vein (veta) between slate and limestone, 

 both rocks being metamorphosed and disturbed. The ore is argentiferous 

 and is distributed tln-ough the entire vein matter. Tlie ordinary ore of the 

 district is livingstonite, a sulphide of antimou}- containing mercury. Cin- 

 nabar is said also to form pseudomorphs after stibnite.' 



Prof. F. Sandb^rger has given a very interesting account of specimens 

 of ore sent to him from Huitzuco by Mr. F. Velten. Tiiey represent a series 

 from fresh stibnite to pseudomorphs of cinnabar after stibnite, containing onl}' 



' I suppose this ininenil to resiiU from the reaction of irou sulphate, produced by the oxidation o( 

 pyrite, ou the limoKtoiie walKs. 



^Anales del niiuisterio de fomeiito, Mexico, vol. 7, ISe'SJ, p. 605. 



'Velten aud Lehmanii: Sitzungsber. k, buyer. AUad. Wiss.,vol. ->, Munich, I8i>7, p.yO-.i, cited by 

 d'Aeliiardi. 



