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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.