The reddish scoriaceous lava in contact with the dyke shows no phenocrysts. The groundmass displays more or less parallel felspar-lathes, ·1 mm. long, augite grains, and much magnetite. The residual glass is fair in quantity; but is mostly gathered into “lakelets” of brown altered glass with sometimes calcite in the centre.
The vitreous border of the dyke is composed of a dark glass quite opaque in the outer portion, but clearer and showing incipient crystallisation in the inner portion.
[40]. Characteristics of Volcanoes, 1890.
[41]. Referred to genus 16 of the olivine-basalts.
[42]. This subject is discussed in [Chapter XXVI.]
[43]. “Na Savu” is the Fijian for waterfall. The complete name of this fall is “Na Savu ni nuku.”
[44]. The flinty concretions are described on page [354], and the iron sand on p. [356].
[45]. Geology of the United States Exploring Expedition.
[46]. A similar arrangement was observed in the columnar basalt of Kauai in the Hawaiian Islands. It is presumed that these Hawaiian flows are sub-aërial.
[47]. The unaltered glass, which incloses a few plagioclase phenocrysts, has a specific gravity of 2·7, and is readily fusible.