is divided geologically into two areas by a fault running from
Rothesay Bay in a south-south-west direction by Loch Fad to Scalpsie Bay,
which, throughout its course, coincides with a well-marked depression. The
tract lying to the north-west of this dislocation is composed of the
metamorphic rocks of the Eastern Highlands. The Dunoon phyllites form a
narrow belt about a mile and a half broad crossing the island between Kames
Bay and Etterick Bay, while the area to the north is occupied by grits and
schists which may be the western prolongations of the Beinn Bheula group.
Near Rothesay and along the hill slopes west of Loch Fad there are parallel
strips of grits and phyllites. That part of the island lying to the east of
this dislocation consists chiefly of Upper Old Red Sandstone strata,
dipping generally in a westerly or south-westerly direction. At the extreme
south end, between Kilchattan and Garroch Head, these conglomerates and
sandstones are overlaid by a thick cornstone or dolomitic limestone marking
the upper limit of the formation, which is surmounted by the cement-stones
and contemporaneous lavas of Lower Carboniferous age. The bedded volcanic
rocks which form a series of ridges trending north-west comprise
porphyritic basalts, andesite, and, near Port Luchdach, brownish trachyte.
Near the base of the volcanic series intrusive igneous rocks of
Carboniferous age appear in the form of sills and bosses, as, for instance,
the oval mass of olivine-basalt on Suidhe Hill. Remnants of raised beaches
are conspicuous in Bute. One of the well-known localities for arctic shelly
clays occurs at Kilchattan brick-works, where the dark red clay rests on
tough boulder-clay and may be regarded as of late glacial age.

As to the origin of the name of Bute, there is some doubt. It has been held
to come from _both_ (Irish for "a cell"), in allusion to the cell which St
Brendan erected in the island in the 6th century; others contend that it is
derived from the British words _ey budh_ (Gaelic, _ey bhiod_), "the island
of corn" (_i.e._ food), in reference to its fertility, notable in contrast
with the barrenness of the Western Isles and Highlands. Bute was probably
first colonized by the vanguard of Scots who came over from Ireland, and at
intervals the Norsemen also secured a footing for longer or shorter
periods. In those days the Butemen were also called Brandanes, after the
Saint. Attesting the antiquity of the island, "Druidical"