side-slabs outside one of the end-slabs, but still under the cover. This
last is a remarkable block of limestone weighing about 70 tons. This
form of tomb is without doubt a link between the simple dolmen and the
corridor-tomb. The portico was at first built under the slab by pushing
an end-stone inwards. Then external side-stones formed the portico,
though still under the slab. The next move was to construct the portico
outside the slab. The portico then needed a roof, and the addition of a
second cover to provide it completed the transition to the simpler
corridor-tomb. In many cases the Irish simple dolmens were surrounded by
a circle of upright stones. At Carrowmore, Sligo, there seems to have
been a veritable cemetery of dolmen-tombs, each of which has one or more
circles around it, the outermost being 120 feet in diameter. The tombs
in these Carrowmore circles were not always simple dolmens, but often
corridor-tombs of more or less complicated types. Their excavation has
not given very definite results. In many cases human bones have been
found in considerable quantities, sometimes in a calcined condition; but
there is no real evidence to show that cremation was the burial rite
practised. The calcination of human bones may well have been caused by
the lighting of fires in the tomb, either at some funeral ceremony, or
in even later days, when the place was used as a shelter for peasants. A
few poor flints were found and a little pottery, together with many
bones of animals and some pins and borers of bone. The most important
find 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 _allée couverte_.]