The soil generally is a sandy loam or a strong but friable clay, and very fertile.
China-clay is white, friable and earthy.
In Mexico, Colombia and Peru the cutting of friable stone with tough volcanic hammers and chisels, as well as rude metallurgy, obtained, but the evidences of smelting are not convincing.
Yet it is in this stratum, and in this alone, that the catacombs are constructed; their engineers avoiding with equal care the solid stone of the tufa litoide and the friable pozzolana, and selecting the stratum of medium hardness, which enabled them to form the vertical walls of their galleries, and to excavate the loculi and cubicula without severe labour and also without fear of their falling in.
It is annual, requires rich but friable soil, grows to about 3 or 4 ft.
It forms a white friable mass which after ignition is insoluble in acids.
Its body is divisible into three portions, an upper capitulum bearing the mouth and tentacles, a median scapus covered by a friable cuticle, and a terminal physa which is rounded.
Volcanic in origin - the Jebel ed-Druz is a group of extinct volcanoes - the friable volcanic soil is extraordinarily fertile.
Often it occurs in the form of irregular friable lumps, like pieces of impure linseed oil-cake.
Its grey houses have a neglected, almost a dilapidated appearance, from the friable stone of which they are constructed; and there are no buildings of antiquarian interest or striking architectural beauty, except, perhaps, the ruined citadel and the remnants of the town walls.