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BOOK II
31
to purplish-white, and cold to the touch. Galen describes it as astringent, moderately acrid, cooling, and useful in reducing swellings. Thus it is similar to most other earths that break up and reduce gatherings. He writes that it is more efficacious than either Chia or Selinusia earths and yet it does not bite. Since it cleans better than Selinusia it is used by fullers. Neither Galen nor Dioscorides mention whether it is porous or dense, light or heavy. A doctor needs only to taste an earth in order to deter­mine its medicinal properties. We can assume this to be soft or intermedi­ate since Pliny, writing about fuller's earths, mentioned a rock which he differentiated from the others by hardness. Dioscorides does not describe Samia aster as hard and if this earth had been hard he would have men­tioned it. In summation, it is moderately unctuous, loose textured, soft, white or purplish-white, sometimes astringent, sometimes acrid.
The earth which physicians call cretica is sometimes meager, sometimes intermediate or even moderately unctuous. A similar earth used in Britain for fertilizer is unctuous since it would have to be in order to make the fields fertile for so many years. That found in Germany is loose-textured and moderately soft although the rock from which it forms is hard. It is white and sufficiently acrid to be detected by the physical senses al­though some is found that is astringent and can be used for cleaning. It resembles Cimolia in that there are different kinds. Cretica earth or chalk, according to Pliny, was placed on the feet of the more important slaves to indicate the ones to be taken home as tokens of victory. Silversmiths use it to clean and polish their wares and for that reason it is sometimes called argentaria. Painters and men who make calculations on tablets of stone or wood use this earth as it makes a white line with ease. Phy­sicians use it since it cleanses and yet does not bite or sting. There are re­gions with hills of chalk in France, Britain, and Muna, a desert island in the Baltic Sea on the route from Pomerania to Copenhagen. The latter rock cannot be used for writing because it is too hard.6 The wall of Constance is built, in great part, of this rock.
Green chalk is similar but is more acrid and cleans better. According to Vitruvius it is found in many places but the best comes from Smyrna. This variety is called θίοδόηοτ after Theodotus who first discovered it. Today it is found in many ore veins and ranks below chrysocolla in color and properties. It is meager, intermediate to slightly unctuous, loose-textured, soft, green, and very slightly acrid. It makes a green line just as white chalk makes a white line.
Paretonium earth is named for a seaport just outside Egypt in Cyrenaica. It is unctuous, dense, and white. Pliny describes this earth when writing about chrysocolla. This is the most unctuous of all the white earths, and, on account of its smoothness, the most tenacious of all those
6 Agricola apparently recognized the relationship between chalk and limestone. Chalk is a soft limestone composed principally of the shells of foraminifera. Lime­stone is a chemical deposit of calcium carbonate.