The fourth period is that in which the various subaerial agencies of abrasion, and especially the streams which drain the mountain chain of the Apennines, have produced the present features of the Campagna, a plain furrowed by gullies and ravines.
5 shows how the octahedron with furrowed edge may be constructed from two interpenetrating tetrahedra (shown in dotted lines).
On the east are furrowed and rugged slopes, rising to the great plateau of the Jaulan (Gaulonitis).
These ridges are separated by longitudinal and furrowed by transverse valleys.
You saw a plain, old-fashioned face, without life or lustre - a figure which had never looked young, and was now prematurely aged; the furrowed face bore witness to concentrated thought.