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have parallel sides, and indefinite, irregular ends. They show parallel extinction; and crushed fragments were determined by the immersion method in liquids of known indices of refraction to have indices very close to those given for orthoclase. Scat- tered phenocrysts of orthoclase have been noted, up to 0-5 mm. by 0-4 mm. Besides orthoclase, a minute grain of a mineral that may be augite was noted in thin section, also small amounts of what appears to be pyrite, in very minute, sometimes cubic grains, frequently arranged in bead-like strings up to 0-03 mm.

Viewed with a binocular microscope, the cavities are seen to be lined with tabular, clear crystals which apparently are felds- par. When these crystals, which are not over 0-25 mm. across, are crushed and observed with the polarizing microscope, they are seen to be microcline, with excellent grating structure, and enclosing minute reddish and deep orange grains of hematite. In these cavities, which are miarolitic in their nature, is also found a colourless, almost isotropic mineral with poor or no cleavage, and an index of refraction considerably less than 1-495. This may be sodalite or analcite.

The texture as seen in thin section is also interesting. The main mass of the rock has the typical divergent texture of the bostonites or trachytes, markedly fluidal in the slides studied. Sections cut from parts of the rock full of the miarolitic cavities show these to be of all shapes and sizes, ranging from a slight disturbance of the usual even-grained texture to a cavity several millimetres in diameter. These cavities are lined with an en- crusting rim made up of radial fibres, inside of which a vacant space occurs, or the space is in some cases filled with feldspar or the mineral noted above as being probably analcite or sodalite. The encrusting radial rims are probably needles of orthoclase or microcline. One or two instances of spherulitic development have been noted, as well as an extension of the radial rims into plumose growths.

The minerals are almost absolutely fresh. The only decom- position noted was a slight oxidation of the pyrite in specimens near the surface. The reddish colouring of the mottled areas appears to be due to submicroscopic matter, probably hematite, enclosed in the feldspar.