The Breadalhane Mines. 199 



longing to this type are of various ages, and are always in 

 stratified rocks. The ores they contain are principally 

 argentiferous galena, zincblende, copper and iron pyrites, with 

 quartz, calcspar, and spathic iron in all proportions, while 

 barytes and other minerals only occur in subordinate 

 quantities. The Clausthal Veins ^ are all in large faults 

 traversing the Culm greywackes and shales, and the ore is 

 often distributed in diagonal bands (Erzfalle), like those 

 developed on a small scale at Tyndrum (Fig. 3). 



The cloud of mystery with which many questions relating 

 to the origin of metalliferous veins are involved, is both thick 

 and heavy to lift, and although miners and engineers have 

 been at work for the last two thousand years, and have 

 honeycombed the earth's crust in search of the precious 

 metals, sometimes to depths exceeding 3000 feet, all their 

 explorations have given us comparatively little help in this 

 department of geological research. One point, however, 

 appears, in some cases, at least, to have been clearly estab- 

 lished, and it is this, that ceteris 'paribus, most metalliferous 

 matter will be deposited at those parts of the vein where the 

 water which holds them in solution, has greatest facility 

 for circulation. In many of the lead veins of Alston Moor 

 on the Tyne, this law has been ascertained by W. Wallace, 

 who has written a treatise on the subject,^ and given many 

 good illustrative drawings and sections of the fissures and 

 veins in that locality. At Tyndrum the law holds good, and 

 the reason why the vein in the quartzites is richest is pro- 

 bably because it is a true fissure vein in which the water 

 could freely circulate, whereas the main vein along the line 

 of fault has been choked up with breccia ted fragments of 

 the soft argillaceous schist, which have effectually obstructed 

 the passage of the metallic solutions. 



Whether the metalliferous matter has come up from below 

 or down from above, or whether it has been infiltrated 

 laterally, is an open question, as no analyses of the adjacent 



^ Described by one of the authors at page 240 of this volume. 



2 "The Laws which regulate the Deposition of Lead Ore in Veins, illus- 

 trated by an examination of the geological structure of the mining districts of 

 Alston Moor." London, 1861. 



