Variolitic Pillow-Lava. — Daly. 71 
several instances that they were flattened so as to lie parallel 
to the true dip, i.e. in the same sense as the pillows themselves. 
Petrography. — The rock in the field is apparently fresh and 
it was expected, in view of the intense glaciation this region 
has suffered and because of the rapidity of wave-erosion at the 
sea-chasm, that extensive alteration of the lavas through weath- 
ering had not taken place. It was therefore hoped that the 
microscope would throw light on the origin of the peculiar 
differentiation of matter in the pillows. But every thin sec- 
tion studied showed that both varioles and matrix have suf- 
fered almost complete decomposition. 
The aphanitic matrix is, in thin section, nearly colorless, 
with a pale green cast. It consists of a confused, structureless, 
massive mat of obscure feldspathic material, accompanied with 
exceedingly abundant calcite and with many ragged colorless 
tremolite or actinolite crystals, much chlorite, zoisite and abund- 
ant yellow grains of epidote. Very rarely one or two minute 
grains or idiomorphic crystals of magnetite will appear in a 
slide. Finally, numerous colorless, isotropic areas occur be- 
tween these various minerals. Such areas may represent orig- 
inal glass, though some of it suggests opal and infiltrated chal- 
cedonic silica. Maximum extinctions in the zone of symmetry 
of the feldspars showed values of about 17°, indicating ande- 
sine. The feldspar is often characterized by radial aggregation. 
With the magnetite and the rather doubtful glass, it represents 
the only original matter in the matrix. 
The varioles seem to be even more completely made up of 
decomposition products. The most prominent constituent oc- 
curs in the form of long, frayed-out skeleton-crystals, shot 
through the generally ground-mass like phenocrysts in an 
igneous base. These crystals vary from o. 1 mm. to 1.0 mm. or 
more in length and from 0.02 to 0.25 mm. in width. They are 
generally bleached to a colorless condition with a correspond- 
ing feathering out into irregular needles of tremolitic habit, 
but, here and there, green and rather strongly pleochroic areas, 
with the characters of actinolite. merge into the colorless am- 
phibole. It is believed that the skeleton-crystals represent 
highly altered actinolite crystals. On account of decomposition, 
they rarely show amphibole cleavage in sections transverse to 
the longer axes of the skeleton-. Along with the bleaching of 
