Bulletin . ?5^r>^y^ (B) Photomicroiirapli of a imlidio,) -^ <^- Shows a U-pilal Su^lStte-c:;^^^ ^f ^1 T * ^^^^ ^-^1-°* ^o- finelainellaM,S-mvth . ^^.^^/^ ^^ «»te similar to thegrowths are etclied it is c ea^lf si o VtL7- ^^^ ^^^^- ^^ ^^^ ^^l i*-are intergrown along e^,-sSnogi\M; dh-eeo;;* ^^^ * *° -^^^Wliitc = chaleocite. Dark = l.„i„ite. VIRGINIA GEOLOGICAL SURVEY. PLATE >yr\YY\ (A) Pliotoruicrograph of a polished section of ore from the Wall mine. Shows atypical example of graphic intergrowth of bornite and chalcocite. Thisstructure is so different from that of
Bulletin . ?5^r>^y^ (B) Photomicroiirapli of a imlidio,) -^ <^- Shows a U-pilal Su^lStte-c:;^^^ ^f ^1 T * ^^^^ ^-^1-°* ^o- finelainellaM,S-mvth . ^^.^^/^ ^^ «»te similar to thegrowths are etclied it is c ea^lf si o VtL7- ^^^ ^^^^- ^^ ^^^ ^^l i*-are intergrown along e^,-sSnogi\M; dh-eeo;;* ^^^ * *° -^^^Wliitc = chaleocite. Dark = l.„i„ite. VIRGINIA GEOLOGICAL SURVEY. PLATE >yr\YY\ (A) Pliotoruicrograph of a polished section of ore from the Wall mine. Shows atypical example of graphic intergrowth of bornite and chalcocite. Thisstructure is so different from that of supergene chalcocite in bornite and soclosely resembles the structures which are characteristic of alloys, mattes, andslags, that the writer, while admitting that it may possibly form as a secondaryprocess, still believes that it is formed in a very different manner from thestructures shown in plates VII and VIII. He believes that such structuresform as a result of hypogene more often than from supergene processes andthat in such cases as this the evidence is far more strongly in favor of ahypogene process and of contemporaneous deposition of the two = chalcocite. Gray = bornite. Black = pits. DETAILED DESCRIPTIOX OF THE VEINS AND ORES. 87 In studying the photomicrographs of the supergene secondary chalcociteand comparing them with those of the hypogene intergrowths of the t
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