They were piled upon each other exactly like courses of hewn stone around the circle which was traced out and care was taken to smooth the beds of the different courses with the knife, and to cut them so as to give the wall a slight inclination inwards, by which contrivance the building acquired the properties of a dome.

The dome was closed somewhat suddenly and flatly by cutting the upper slabs in a wedge-form instead of the more rectangular shape of those below.

The roof was about eight feet high, and the last aperture was shut up by a small conical piece.

The whole was built from within and each slab was cut so that it retained its position without requiring support until another was placed beside it, the lightness of the slabs greatly facilitating the operation.

When the building was covered in a little loose snow was thrown over it to close up every chink and a low door was cut through the walls with a knife.