Bulletin . hoth hypo-gene or primary minerals and that they are of contemporaneous deposition. The writer believes that such crystallographic intergrowths are formedonly when the component minerals are of contemporaneous deposition, andthat they are similar to the same type of intergrowths in pegmatite, othersulphide intergrowths, such as sphalerite and pyrite, galena, argentite, andbismuthinite, galena and stibnite, and many others, and to the eutecticand eutectoid intergrowths of sulphides in mattes and of metals in alloys,all of which produce the same type of pattern. So far as the writerse
Bulletin . hoth hypo-gene or primary minerals and that they are of contemporaneous deposition. The writer believes that such crystallographic intergrowths are formedonly when the component minerals are of contemporaneous deposition, andthat they are similar to the same type of intergrowths in pegmatite, othersulphide intergrowths, such as sphalerite and pyrite, galena, argentite, andbismuthinite, galena and stibnite, and many others, and to the eutecticand eutectoid intergrowths of sulphides in mattes and of metals in alloys,all of which produce the same type of pattern. So far as the writersexperience has extended such intergrowths have never been found to havefoi-med as the result of supergene agencies and processes. »Laney, Francis Baker: The relation of bornite and chalcocite in the copperores of the Virgilina district of Xorth Carolina and Virginia, Proc. U. S. NatlMuseum, Vol. 40. 1911. pp. 413-424: ibidem. Economic Geologv, Vol. 6, 1911, VIRGINIA GEOLOGICAL SURVEY. PLATE .1 (A) Photomicrograph of a polished section of ore from Cornfield Prospect No. chalcocite of two distinct shades of color, one a delicate hluish gray,and the other normal. The bluish gray chalcocite is in graphic intergrowthwith bornite which shows in the photographs as irregular areas, as minutedots, and in elongated rod-like forms. The two ehalcocites are not clearlydifferentiated from each other in the photograph, but are easily distinguish-able by the eye. The eAidence as to the origin of such structures is not con-clusive, but the writer believes the minerals were deposited gray ^ chalcocite. Dark gray ^ bornite. VIRGINIA GEOLOGICAL SURVEY. PLATE XIX.
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