d made, however, was a small conical button made of bone with two
holes pierced in its flat side and meeting in the middle. It is a type
which occurs in Europe only at the period of transition from the age of
stone to that of bronze, and usually in connection with megalithic
monuments.

[Illustration: FIG. 6. Type-plan of the simple rectangular corridor-tomb
or _allee couverte_.]

We pass on now to consider the simplest form of corridor-tomb, that in
which there are several cover-slabs, but no separate chamber (Fig. 6).
These tombs occur in most parts of Ireland. At Carrick-a-Dhirra, County
Waterford, there is a perfect example of the most simple type. The tomb
is exactly rectangular and lies east and west, with a length of 19 feet
and a breadth of 7-1/2. At each end is a single upright, and each long
side consists of seven. The chamber thus formed is roofed by five slabs.
The whole was surrounded by a circle of about twenty-six stones, and no
doubt the chamber was originally covered by a mound. In a somewhat
similar example at Coolback, Fermanagh, the remains of the elliptical
cairn are still visible.

But in most cases the plan of the corridor-tomb is complicated by a kind
of outer lining of blocks which was added to it. Most of the monuments
are so damaged that it is difficult to see what the exact form of this
lining was. Whether it merely consisted of a line of upright blocks
close around the sides of the chamber or whether these supported some
further structure which covered up the whole chamber it is difficult to
say. In some cases the roof-slab actually covers the outer line of
blocks, and here it seems certain that this outer line served simply to
reinforce the chamber walls, the space between being filled with earth
or rubble. However, at Labbamologa, County Cork, is a tomb called Leaba
Callighe, in which this was certainly not the case. The length of the
whole monument is about 42 feet. The slabs cover the inner walls of the
chamber, but not the outer lining: this last forms a kind of outer shell
to the whole monument. It is shaped roughly like a ship, and runs to a
point at the east end, thus representing the bow. The west end is
damaged, but may have been pointed like the east. The whole reminds one
very forcibly of the _naus_ of the Balearic Isles and the Giants' Graves
of Sardinia. Occasionally the corridor-tomb has a kind of portico at its
west end.

[Illustration: FIG. 7. Type-plan of