454 
PLF^T'S KATFRAL HISTOEY. 
[Book XYII. 
earth. These stones are broken upon the land itself, and it is 
with considerable difficulty during the earlier years that the 
stalk of the corn is cut, in consequence of the presence of these 
stones ; however, as it is remarkably light, it only costs for 
carriage one-half of the outlay required in using the other 
varieties. It is laid but very thinly on the surface, and it is 
generally thought that it is mixed with salt. Both of these 
varieties, when once laid on the land, will fertilize it for 
fifty "^^ years, whether for grain or for hay. 
(8.) Of the marls that are found to be of an unctuous na- 
ture, the best is the white. There are several varieties of it : 
the most pungent and biting being the one already mentioned. 
Another kind is the white chalk that is used for cleaning 
silver ; it is taken from a considerable depth in the ground, 
the pits being sunk, in most instances, as much as one hundred 
feet. These pits are narrow at the mouth, but the shafts en- 
large very considerably in the interior, as is the case in mines; 
it is in Britain more particularly that this chalk is employed. 
The good elfects of it are found to last full eighty years ; and 
there is no instance known of an agriculturist laying it twice 
on the same land during his life.^^ A third variety of white 
marl is known as glisomarga it consists of fullers' chalk 
mixed with an unctuous earth, and is better for promoting the 
growth of hay than grain ; so much so, in fact, that between 
harvest and the ensuing seed-time there is cut a most abundant 
crop of grass. While the corn is growing, however, it will 
allow no other plant to grow there. Its effects will last so 
long as thirty years ; but if laid too thickly on the ground, it 
is apt to choke up the soil, just as if it had been covered with 
Signine^^ cement. The Gauls give to the columbine marl in 
Marl does not begin to fertilize tiU several years after it has been laid 
down ; hence, it is generally recommended to marl the land a little at a 
time, and often. If the ground is fully marled, it requires to be marled 
afresh in about eight or ten years, and not fifty, as Pliny says. 
80 a Argentaria." Used, probably, in the same way as whitening in 
modern times. See B. xxxv. c. 58. 
^1 An exaggeration, no doubt. 
^2 Probably meaning " smooth marl ; " a variety, Fee thinks, of argil- 
laceous marl, and, perhaps, the potter argillaceous marl, or potter's argil. 
He suggests, also that it may have possibly been the Marga fuUonum 
saponacea lamellosa of Valerius ; in other words, fullers' earth. 
Creta fullonia. 
6^ See B. xxxv. c. 46, 
