BOOK XVII. IV. 45-48
a narrow mouth but with the shaft expanding in the interior, as is the practice in mines. This chalk is chiefly used in Britain. Its effect lasts for 80 years, and there is no case of anybody having scattered it on the same land twice in his lifetime. A third kind intermixed with a greasy earth, and it is a more effective, white marl is called glisomarga; this is fullers' chalk more dressing for pasture than for corn, so that, when a crop of corn has been carried, before the next sowing a very abundant crop of hay can be cut, although while growing corn the land does not produce any other plant. Its effect lasts 30 years; but if it is scattered too thickly it chokes the soil just as Segni plaster does. For dove-coloured marl the Gallic provinces have a name in their own language, eglecopala; it is taken up in blocks like stone, and is split by the action of sun and frost so as to form extremely thin plates. This kind of marl is equally beneficial for corn and grass. Farmers use sandy marl if no other is available; but they use it on damp soils even if another sort is available. The Ubii are the only race known to us who while cultivating extremely fertile land enrich it by digging up any sort of earth below three feet and throwing it on the land in a layer a foot thick; but the benefit of this top-dressing does not last longer than ten years. The Aedui and the Pictones have made their arable land extremely fertile by means of chalk, which is indeed also found most useful for olives and vines. But all marl should be thrown on the land after it has been ploughed, in order that its medicinal properties may be absorbed at once; and it requires a moderate amount of dung, as at first it is too rough and is not diffused into vegetation; otherwise whatever
