BOOK XVII. IV. 42-45
name of leucargillum to a white clay that they use on the land at Megara, but only where the soil is damp and chilly. The other substance brings wealth to the provinces of Gaul and Britain, and may suitably receive a careful description.
There had previously been two kinds of marl, but recently with the progress of discoveries a larger number have begun to be worked: there is white marl, red marl, dove-coloured marl, argillaceous marl, tufa marl and sand marl. It has a twofold consistency, rough or greasy, each of which can be detected by its feel in the hand. Its use is correspondingly double, to feed cereals only or to feed pasture-land as well. Tufa marl nourishes grain, and white marl, if it is found where springs rise, has unlimited fertilizing properties, but it is rough to handle, and if it is scattered in excessive quantities it scorches up the soil. The next kind is the red marl, which is known as acaunumarga,a consisting of stone mingled with a thin, sandy earth. The stone is crushed on the land itself, and in the earliest years of its employment the fragments make the cornstalks difficult to cut; however, as it is extremely light it can be carried for only half of the cost charged for the other varieties. It is scattered on the land thinly; it is thought to contain a mixture of salt. With both of these kinds a single scattering serves for fifty years to fertilize either crops or pasture.
Of the marls that are greasy to the touch the chief one is the white. §§ 43-44.It has several varieties, the most pungent being the one mentioned above. Another variety of white marl is the chalk used for cleaning silver; this is obtained from a considerable depth in the ground, usually from pits made 100 feet deep, with