Bulletin of the Geological Society of America . In the glass are embedded the undissolved grainsof the original minerals, which may vary in amount from about one-halfof the whole mass to a very small fraction of it. In places, then, therock has been converted almost completely to glass, in which case themass is light colored and of a pale yellow in thin section. As the extentof fusion diminishes, the glass becomes darker and more nearly refractive index of the glass varies somewhat, but is never far from XXIX—Bull. Geol. Soo. Am., Vol. 34, 1922 434 BOWEX AND AUROUSSEAU FUSION OF SED
Bulletin of the Geological Society of America . In the glass are embedded the undissolved grainsof the original minerals, which may vary in amount from about one-halfof the whole mass to a very small fraction of it. In places, then, therock has been converted almost completely to glass, in which case themass is light colored and of a pale yellow in thin section. As the extentof fusion diminishes, the glass becomes darker and more nearly refractive index of the glass varies somewhat, but is never far from XXIX—Bull. Geol. Soo. Am., Vol. 34, 1922 434 BOWEX AND AUROUSSEAU FUSION OF SEDIMENTARY ROCKS Such selective action during fusion as is in evidence is mainlyconnected with the size of grain rather than with the nature of the ma-terial. The residual undissolved grains are the larger grains of practi-cally all the minerals present, and the ready getting together of the finergrains to effect mutual fluxing has evidently been the important factorin facilitating fusion. Quartz and plagioclase are the more persistent,. Figure 2.—Thin-section of fused Core, Montezuma Mell Xumler 1 Crossed nicols. The dark areas are glass, the bright patches undissolved grains ofquartz and plagioclase. Twinned plagioclase at center. as they are the larger grains, but the quartz is apparently not more per-sistent than j)lagioclase. It is not impossible, however, that the very fineso called clayey matter may be intrinsically more fusible. Occasionalsmall fragments of metallic iron from the pipe are to be found in the glass. MICROSCOPIC CHARACTERS OF CORE MATERIAL 435 In most of the glass there is a moderate amomit of separated crystals are not definitely identifiable, but appear to con-sist largely of. minute needles of sillimanite. Close to the iron pipe thereis a fairly conspicuous development of fayalite in small but definitelydeterminable grains of very high birefringence and minimum refractiveindex about Chemical Character oe the Core Mate
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
