Sometimes they occupy the approaches to tablelands, the narrowest points of gorges, or the fords of rivers; sometimes almost inaccessible mountain tops or important points on ridges; and it may be noticed that, where two important nuraghi are not visible from one another, a small one is interpolated, showing that there was a system of signalling from one to another.
Its weight varies from 48 to about 55lb the cubic foot, but in very hard slowly-grown trunks sometimes approaches 60 lb.
An intelligent creature, or "demon," possessed of unlimited powers of vision, is placed in charge of each door, with instructions to open the door whenever a particle in A comes towards it with more than a certain velocity V, and to keep it closed against all particles in A moving with less than this velocity, but, on the other hand, to open the door whenever a particle in B approaches it with less than a certain velocity v, which is not greater than V, and to keep it closed against all particles in B moving with a greater velocity than this.
The central range here approaches much nearer to the sea, and hence, with few exceptions, the rivers that flow from it have short courses and are of comparatively little importance.
The Bergamo sheep is the largest breed in the country; that of Cadore and Belluno approaches it in size.