Transactions . s an ordinary pctrographicalmicroscope. Blue-prints were then made from the negatives and inked in on thelines of the photograph with water-proof ink. The blue-prints were then placedin a weak solution of sodium carbonate, which bleached them, except for a faint GEOLOGY OF THE MAGNETITES NEAR PORT HENRY, N. Y. 177 of the relations. It may be well to explain that microperthiteis a name applied to a variety of feldspar, particularly ortho-clase, that has as inclusions flattened spindles of some otherfeldspar, especially albite, in parallel alignment, so that thelatter may even con
Transactions . s an ordinary pctrographicalmicroscope. Blue-prints were then made from the negatives and inked in on thelines of the photograph with water-proof ink. The blue-prints were then placedin a weak solution of sodium carbonate, which bleached them, except for a faint GEOLOGY OF THE MAGNETITES NEAR PORT HENRY, N. Y. 177 of the relations. It may be well to explain that microperthiteis a name applied to a variety of feldspar, particularly ortho-clase, that has as inclusions flattened spindles of some otherfeldspar, especially albite, in parallel alignment, so that thelatter may even constitute the larger part of the aggregate. The microperthite occurs in irregular grains and at timescontains rounded inclusions of quartz, indicating a successionof the minerals in order of formation the reverse of that in theusual igneous rock, the quartz, if it is a real inclusion, havingformed before the feldspar. These relations are common inmetamorphic rocks and lead one to infer that the gneiss has Fig. 21 gneiss ; ordinary light; actual field, mm. = in. The clear mine-ral is quartz ; the shaded one feldspar. The shading is purely conventional. Thespindles of albite in the micro-perthite are self-evident. The black is magnetite. gone through some process of recrystallization. During this,the quartz and feldspar may have crystallized at the same time,or the quartz may have resulted from some secondary change inthe original feldspathic compound. Microperthite itself is morecommon in metamorphic rocks than in unchanged igneousones, although it appears to be not unknown in the latter.* It brown tinge, and afterwards in very dilute hydrochloric acid, which turned thebrown pale blue, leaving the black ink on a white or pale blue (actinically white)ground. In this way the accuracy of a photograph is preserved, together withthe distinctness of a pen drawing. Photomicrographs of rock sections are other-wise very unsatisfactory because of their flatness and failure to bri
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
