Note note 13, p. 233 — BOOK VII.

[13] Tophus. (Interpretatio, Toffstein oder topstein). According to Dana (Syst. of Min., p. 678), the German topfstein was English potstone or soapstone, a magnesian silicate. It is scarcely possible, however, that this is what Agricola meant by this term, for such a substance would be highly infusible. Agricola has a good deal to say about this mineral in De Natura Fossilium (p. 189 and 313), and from these descriptions it would seem to be a tufaceous limestone of various sorts, embracing some marls, stalagmites, calcareous sinter, etc. He states: "Generally fire does not melt it, but makes it harder and breaks it into powder. Tophus is said to be a stone found in caverns, made from the dripping of stone juice solidified by cold ... sometimes it is found containing many shells, and likewise the impressions of alder leaves; our people make lime by burning it." Pliny, upon whom Agricola depends largely for his nomenclature, mentions such a substance (XXXVI, 48): "Among the multitude of stones there is tophus. It is unsuitable for [Pg 234]buildings, because it is perishable and soft. Still, however, there are some places which have no other, as Carthage, in Africa. It is eaten away by the emanations from the sea, crumbled to dust by the wind, and washed away by the rain." In fact, tophus was a wide genus among the older mineralogists, Wallerius (Meditationes Physico-Chemicae De Origine Mundi, Stockholm, 1776, p. 186), for instance, gives 22 varieties. For the purposes for which it is used we believe it was always limestone of some form.