412 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



It seems to rae that deposits of this description may conveniently 

 be called chaiuhered veins and that the irregular, excrescent bodies of ore 

 of such de})osits may fitly be denominated vein chamhers. I propose these 

 terms to expi-ess the external form only and to embrace irregular ore 

 bodies contiguous with a fissure, whether they consist of reticulated 

 masses, of impregnations, or ore deposited l)y substitution. A cliandjered 

 vein may then be defined as a deposit consisting of an ore-bearing fis- 

 snre and of ore bodies contiguous with the fissure which extend into the 

 country rock. The term is intended for use in contradistinction to the term 

 fissure vein, or, more explicitly, simple fissure vein, which is thus restricted 

 to those cases in which tlie occurrence of ore is limited to a single defined 

 fissure. Transitions between the two forms are not infrequent, and such 

 occurrences may be referred to conveniently as veins which are to some 

 extent chambered or which show a tendency to chambering.' 



Cap chambers — In grauitcs aucl gucisses it is not infrequently the case that 

 simple fissure veins are found which fi'om the cropping downward are very 

 regular. I doubt, however, whether, if in these cases the siuface still re- 

 mained as it existed at the time when the fissure was formed, the su])erior 

 2>ortion of the deposits would be found to possess an equal degree of regu- 

 larity. Wlten a fissure is formed a fault almost or quite invai-iably accom- 

 panies it, for it is a force tending to elevate one portion of a region above 

 another which usually produces the fissure. When a fault takes place, it is 

 well known that the hanging country is conmionly depressed relativel}" to 

 tlfe foot-wall and a projecting edge of the hanging ground nuist then press 

 and scrape against the foot-wall. This wedge like mass, not being sup- 

 ported at the surface by overlj'ing rock, is greatly exposed to fracture, and 

 will generally be more or less fissured, even when it is composed of firm 

 material, such as granite. If ore deposition follows from solutions which 

 reach the upper part of such a fissure, the irregular cracks in the lip of the 

 hanging country will fill with vein matter and tlie simple vein will be sur- 

 mounted by a chamber or a series of chambers close to the surface. 



' "Cliainl)ere'l veins" seems to be as n.atiiral .and as appropriate ,a term as the familiar "cliaml)ered 

 slicU;" indeed, the analogy between them is a close one, for the siphnncle which passes throngh the 

 chambers of the nautilus and of other tetr.abra:iohiata answers to the (issure of a chambered vein. 



