of wood, even where their walls were of
stone;" while in the oratories or primitive smaller stone churches, "the
roofs (says he) generally appear to have been constructed of stone,
their sides forming at the ridge a very acute angle."[88] The selection
of the special materials of which both walls and roof were composed, was
no doubt, in many cases, regulated and determined by the comparative
facility or difficulty with which these materials were obtained. At no
time, perhaps, did timber exist on Inchcolm that could have been used in
constructing such a building; whilst plenty of stones fit for the
purpose abounded on the island, and there was abundance of lime on the
neighbouring shore. Stone-roofed oratories of a more complex and
elaborate architectural character than that of Inchcolm still exist in
Ireland, and of a supposed very early date. We have already found, for
instance, Dr. Petrie stating that "we have every reason to believe" that
the stone-roofed oratories known as St. Kevin's House at Glendalough,
and St. Columba's House at Kells, "were erected by the persons whose
names they bear,"[89] and consequently that they are as old as the sixth
century. These two oratories, are, as it were, two storeyed buildings;
for each consists of a lower and larger stone-arched or vaulted chamber
below, and of another higher and smaller stone-arched or vaulted chamber
or over-croft above. The old small stone-roofed church still standing at
Killaloe, and the erection of which Dr. Petrie is[90] inclined to
ascribe to St. Flannan in the seventh century[91] presents also in its
structure this type of double stone-vault or arch, as shown in the
following section of it by Mr. Fergusson.[92] When treating of the early
Irish oratories, Mr. Fergusson observes, "One of the peculiarities of
these churches is, that they were nearly all designed to have stone
roofs, no wood being used in their construction. The section (Fig. 11)
of the old church at Killaloe, belonging probably to the tenth century,
will explain how this was generally managed. The nave was roofed with a
tunnel-vault with a pointed one over it, on which the roofing slabs were
laid." Mr. Fergusson adduces Cormac's Chapel on the Rock of Cashel, St.
Kevin's House or Kitchen at Glendalough, which he thinks "may belong to
the seventh century;" and St. Columba's House at Kells, "and several
others in various parts of Ireland, as all displaying the same
peculiarity" in the stone ro