The cap-stone is often from thirty to forty feet in circumference, and eight to ten feet in length, the side of it which is turned underneath, and forms the roof of the chamber, has always a smooth flat surface, while the side turned uppermost is almost always of a very irregular form. The supporting stones are also flat only on the side which is turned to the chamber. They commonly fit close to each other, the small openings which, from the nature of the material, may occur between them, being stopped up with flat pieces of stone placed one upon the other. The usual height of the supporting stones is from six to eight feet, and their breadth from two to three feet; their number depends on the height of the chamber; they are usually from four to five, but occasionally about fifteen have been met with in one of those structures; whence it follows that such a chamber must have had more than one roofing stone. The floor of the chamber itself is paved partly with flat stones, and partly with a number of small flints which appear to have been exposed to a very powerful heat. The chambers are either quite round, from five to seven feet in diameter, or they are oval and from twelve to sixteen feet in length, or they are merely formed of their supporting stones, so placed, that the two longest form the side walls and the shortest the cap-stone at the end.
Entrances of regular form, enclosed with blocks of stone, provided with a roof, and leading to the chambers of the long cromlechs, are very rare and are met with only in the largest of them. There is in general an opening between two of the supporting stones, which is sometimes indicated externally by two flat stones placed upright, or occasionally by a row of stones placed along the side of the hill and leading to such entrance. Like the hill itself there is no rule as to the direction in which it is placed; in most cases it has a direction south and east, and occasionally south-east, south- west, and north.
The most important of these monuments are the long-cromlechs, which consist of three chambers, a large one in
