OF THE RIO-TTXTO MINES. 255 



natural liquor issuing from the mines, and (K) of the liquor flowing 



from the cementation-tanks. Each of these is found to deposit 

 iron-oxide wherever the waters are checked so as to allow of natural 

 oxidation and evaporation. 



J. Natural hquor. K. Sahda hquor. 



Ferrous sulphate 4-091 54-276 grams per litre. 



Eerric sulphate -030 6-075 „ 



Aluminic sulphate -504 '800 „ 



^langanous sulphate .... -003 -016 „ 



Zincic sulphate -308 2-814 



Cupric sulphate 1*761 -282 



Plumhic sulphate -009 -040 



Calcic sulphate '259 1*026 „ 



Magnesic sulphate ...... -066 -312 „ 



Potassic sulphate -023 -020 „ 



Sodic sulphate -052 -040 



Sulphuric acid (free) .... 1-274 "752 „ 



Sodic chloride -017 '039 



Antimony and hismuth . . traces. traces. „ 



Arsenic '. . -028 -078 



Silica -074 -026 



?» 



8-505 66-596 



Pyntes. — The pyrites-masses are almost always contact-deposits, 

 i. e. they occupy the enlarged portions of fissures separating two 

 dissimilar rocks. Occasionally, it is true, hoth walls of a mass are 

 composed of the same rock for a short distance, in vertical or hori- 

 zontal extension, owing to the fact that the fissure has been made 

 more nearly in a plane than is the bounding-surface of the two 

 rocks, a phenomenon which has been frequently observed in other 

 districts*. Some few of the deposits, however, appear to be con- 

 tained wholly in slate, and others wholly in porphyry, but never far 

 from a junction of these dissimilar rocks. 



The enlarged portions of the pyrites-lodes of Rio Tinto and other 

 parts of the Sierra Morena, it seems to me, only diff'er in degree 

 from the " shoots " and " courses of ore " observable in connexion 

 with fissure-lodes in other countries. Owing to the lenticular 

 character of the porphyritic intrusions which occupy the original lines 

 of weakness, and which have occasioned those openings which now 

 form the lode-fissures, the junctions between the slate and the por- 

 phyry are subject to considerable inflections (see map, Plate TI.) ; and 

 although the more recent openings which now contain the pyrites 

 have not followed these junctions everj-where exactly, still the 

 result has been to produce fissures somewhat more made up of varj-ing 

 directions than is observable where a simple country-rock has been 

 fissured. 



* See Foster " On the Great Flat Lode," Quart. Journ. Geol. Soc. vol. xxxiv. 

 p. 640. 



