ent, thus consisting of
plagioclase and mica, with a little magnetite. Quartz may be an
accessory. This rock occurs amongst the Lower Silurian strata of
Ireland, Cumberland, and the South of Scotland; it is not volcanic in
the ordinary acceptation of that term. The term _lampophyre_ was
introduced by Guembel in describing the mica-traps of Fichtelgebirge.

8. ANDESITE.--This is a dark-coloured, compact or vesicular,
semi-vitreous group of volcanic rocks, composed essentially of a glassy
plagioclase felspar, and a ferro-magnesian constituent enclosed in a
glassy base. According to the nature of the ferro-magnesian constituent,
the group may be divided into _hornblende-andesite_, _biotite-andesite_,
and _augite-andesite_. Quartz is sometimes present, and when this
mineral becomes an essential it gives rise to a variety called
_quartz-andesite_ or _dacite_.

These rocks are the principal constituents of the lavas of the Andes,
and the name was first applied to them by Leopold von Buch; but their
representatives also occur in the British Isles, Germany, and elsewhere.
Dacite is the lava of Krakatoa and some of the volcanoes of Japan.

9, 10. TRACHYTE and DOMITE, etc.--These names include very numerous
varieties of highly silicated volcanic rock, and in their general form
consist of a white felsitic paste with distinct crystals of sanidine,
together with plagioclase, augite, biotite, hornblende, and accessories.
When crystalline grains or blebs of quartz occur, we have a
quartz-trachyte; when tridymite is abundant, as in the trachyte of Co.
Antrim, we have "tridymite-trachyte."

The trachytes occupy a position between the pitchstone lavas on the one
hand, and the andesites and granophyres on the other.

(_b._) _Domite_ is the name applied to the trachytic rocks of the
Auvergne district and the Puy de Dome particularly. They do not contain
free quartz, though they are highly acid rocks, containing sometimes as
much as 68 per cent. of silica.

(_c._) _Phonolite (Clinkstone)_ is a trachytic rock, composed
essentially of sanidine, nepheline, and augite or hornblende. It is
usually of a greenish colour, hard and compact, so as to ring under the
hammer; hence the name. The Wolf Rock is composed of phonolite, and it
occurs largely in Auvergne.

(_d._) _Rhyolites_ are closely connected with the _quartz-trachytes_,
but present a marked fluidal, spherulitic, or perlitic structure. They
consist of a trachytic ground-mass in whi