THEIR CONTENTS AND DIRECTIONS. 105 



In some instances the vein-stuff consists of a single sub- 

 stance in repeated coatings, such as quartz or carbonate of 

 lime ; in other instances it is made up of alternating layers 

 of two substances, such as lime and baryta ; and in many 

 cases it consists of a seemingly capricious admixture of 

 several ingredients. As with the vein-stuffs so with the 

 enclosed metallic ores some veins containing only one 

 metal, others two or more metals, and in such cases there 

 is usually a curious and persistent connection, as lead with 

 silver, copper with tin, iron with manganese, and gold with 

 platinum. Besides this curious connection of metal with 

 metal, there is often an observed relation between certain 

 ores and certain vein-stuffs, as gold in quartz, lead in car- 

 bonates and fluates of lime, &c. ; and these relations when 

 carefully noted are often of great practical value to the 

 mineral explorer. What has caused these curious alterna- 

 tions of vein-stuffs and connections of certain metals science 

 cannot in the mean time determine, but it observes the 

 modes in which they occur, and this, when accurately done, 

 is always a step towards the solution. Whatever the causes, 

 they have operated not always in filling the veins and fis- 

 sures merely, but often in impregnating the adjacent rocks 

 through which the veins pass, and thus the cheeks or walls 

 are occasionally worked for the strings and plates of the 

 ores they contain. 



But though unable to explain the relations of certain 

 ores to certain vein-stuffs, geology has amassed a great 

 deal of observation on the subject, as well as on the preva- 

 lent direction or strike which veins take in certain locali- 

 ties. The ascertaining of this direction is all-important; 

 for while the main veins of a district containing one kind 

 of metal are found to strike always in one direction 

 easterly and westerly, for instance the secondary or cross 

 veins running northerly and southerly are almost certain to 



