226 NICOLAUS STENO 



characteristics of the other's surface, it will be easy, granted 

 a solid and the place in which it is, to affirm something definite 

 about the place of its production. And this, indeed, is the 

 general question of a solid contained within a solid. 



I pass to the more particular investigation of those solids dug 

 from the earth which have given rise to many disputes ; espe- 

 p. 26. cially incrustations, deposits, angular bodies, the shells of marine 

 animals, of mollusks, and the forms of plants. Under incrusta- 

 tions belong rocks of ever)f kind consisting of layers, whose 

 two surfaces are indeed parallel but not extended in the same 

 plane. The place where incrustations are formed is the entire 

 common boundary of fluid and solid ; and the result is that the 

 form of the layers or crusts corresponds to the form of the 

 place, and it is easy to determine which of them hardened first, 

 which last. For if the place was concave, the outer layers were 

 formed first; if convex, the inner ;i if the place was uneven 

 because of various larger projections, the new layers were pro- 

 duced in the larger spaces when the narrower spaces had been 

 filled with the formation of the first layers. 



From this fact it is easy to account for all the differences of 

 form which are seen in sections of similar rocks, whether they 

 show the round veins of a tree cut transversely, or resemble the 

 sinuous folds of serpents, or run along, curved in any other way, 

 without law. Nor is it surprising that agates and other kinds 

 of incrustations seem, so far as regards their outer surface, 

 rough like ordinary stones,^ since the outer surface of the outer 

 layer imitates the roughness of the place. In torrents, however, 

 incrustations of this kind are more frequently found outside of 

 the place of their production, because the matter of the place 

 has been scattered by a breaking up of the strata. 



Concerning the manner in which particles of the layers 

 p. 26. which are to be added to a solid are separated from the fluid, 

 the following at least is certain : 



^ The reference is doubtless to the formation of secretions in the first instance, and con- 

 cretions in the second. 



^ The Florentine edition reads saxis ignobilis instar asperos ; this is partially corrected in 

 the Leyden edition of 1679 to saxi, etc. The correct reading saxiignobilis instar asperas is 

 given by Maar, op. cit., Vol. II, p. 196. 



