454 PLINY'S NATURAL HISTORY. [Book XVII. 



earth. These stones are broken npon 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 79 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 80 

 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 effects 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. 81 A third variety of white 

 marl is known as glisomarga ; 83 it consists of fullers' chalk 83 

 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 84 cement. The Gauls give to the columbine marl in 



79 Marl does not begin to fertilize till 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. 



so « Argentaria." Used, probably, iu the same way as whitening in 

 modern times. See B. xxxv. c. 58. 



81 An exaggeration, no doubt. 



92 Probably meaning " smooth marl ; " a variety, Fee thinks, of argil- 

 laceous marl, and, perhaps, the potter's argillaceous marl, or potter's argil. 

 He suggests, also that it may have possibly been the Marga fullonum 

 saponacea lamellosa of Valerius ; in other words, fullers' earth. 



83 Creta follonia. 



84 See B. xxxv. c. 46. 



