Volltext Seite (XML)
Argillite. 235 quefttly thin, more or lefs difficultly feparable, fometimes approac.hing to the foliated. Frag ments, 2, lrequently rabular; fometimes long fplintery, rarely trapezoidal, or rhomboidal. I-Jardnefs, from 5 to 8. Sp. gr. froin 2,67 to 2,88; but generally from 2,7 to 2,8. Lafius mentions one of a pcarl grey colour, whofe fp. gr. is but 2,500; Hartz 109. The heavier contain an excefs of iron. It gives a white or grey ftreak, fometimes a reddifh grey. It does not adhere to the tongue. Ic does not ftain, yet Lafius mentions one fo foft as to lcave a white line, on harder ftones. Ibid. It is compofed of filex, argill, calx, magnefia, and iron with fome bituminous particles; the proportions nearly in the order I have mentioned, when the mean of all the varieties is confidered; but, in the different varieties, the proportion va- ries confidcrably; and hence the numerous varie- tics ofthis fpecies: with thefe, mica or talc is often intimately incorporated. Its tranfitions are into fandftone, filiceous fhiftus, jafper, hornftone, grau-w.acken, fyenite, ihifto^e hornblende, fhiftofe porphyry. Very commonly itimbibes water, but different varieties abforb it in various proportions. It fometimes bears impreffions of vegetables, fometimes of fhells. It differs from (late clay, in the form of its furface, hardnefs, fpcc. gravity, relation to wa ter, and inadhefion to the tongue, as well as in qompofition, containing more magnefia and iron. The