244 PROCEEDINGS OF SECTION C. 
mining three fairly well defined zones were exploited—the 
upper zone, in which copper alone was won; the middle 
zone, in which both tin and copper became the object of 
mining; and the bottom zone, in which tin alone was won. 
C. Le Neve Foster* illustrates this very well in a projection 
of the famous Dalcoath lode. The three zones are seen to 
lie nearly horizontally one above the other. The lode also 
changes its wall-rock in depth, the upper levels being mostly 
in slate (killas) and the lower levels in granite. But the 
diagram shows distinctly that the change in metallic content 
is totally independent of the change of country, for at the 
eastern end of the mine workings the granite lives nearly up 
to the surface, whereas the change in mineral contents has 
taken place at the usual level. This change of character 
with depth in the case of the Cornish tin mines is most 
suggestive of the way in which the same solutions, emana- 
ting from eruptive magmas, may give rise to deposits of 
a totally different metallic content. Many other lodes in 
Cornwall show a similar alteration in depth. At the sur- 
face they are either copper veins or copper-tin veins, the 
former being as a rule closer to the periphery of the granite 
masses than the latter. 
Vogt describes} anumber of copper deposits in the district 
of Thelemarken, Norway, which present some remarkable 
similarities to tin veins. They are, in fact, as he remarks, 
‘tin veins with copper ore instead of tin.” Mineralogically 
they are characterised by the minerals chalcopyrite, bornite, 
chalcocite, with here and there specularite, galena, and zinc- 
blende, fahlerz, ores of arsenic, bismuth, and uranium, native 
gold, silver, and copper, titanic iron ore, rutile, &c., in com- 
bination with quartz, muscovite, calcite, dolomite, and fluor- 
spar (sometimes so massive that it becomes the object of 
mining) ; further, tourmaline, and, in smaller quantities, 
beryl and apatite. The deposits occtir in connection with 
dykes of granite, and the latter, in the vicinity of the veins, 
has been converted into an almost typical greissen. 
Silver-Lead Veins. 
C. R. Keyes{ describes a group of silver-lead veins in the 
Mississippi Valley, 20 miles east of Ironton, Missouri, which 
bear upon this subject. The wall-rock is the common coarse- 
grained red granite of the region, composed chiefly of ortho- 
clase and quartz, with some biotite and plagioclase. The 
veins vary in width from three to five feet, and the country- 
rock on each side of the vein has been converted into a 
* Mining, 1883, p. 452. 
7:Z. £.°P.G.,° 1895)" ps 149. 
t Diverse origins, &c. Trans. Am. Inst. M. Eng., Nov., 1901. 
