38 SURFACE OF THE EARTH. meadow-ore, fwamp-ore, morafs-ore, &c.: that many of thefe form beds, which are thicker or thinner according as the precipitates have been more or lefs copious: that thefe beds are more or lefs inclined, correfponding in this refpeCt to that of the bottom on which they are depofited : that they alfo fill up rents or fifiures in the ftrata, and thus form folid and compact veins : that they contain petrifactions of various kinds. Thefe faCts alfo fhew, that many chemical formations are ftill going on, on the furface of the earth, and that many more took place in former times. 31. We lhall finilh this fubjed, by mentioning the characters by which fubftances formed from a ftate of chemical folution, are to be diftinguilhed from thofe formed by depofition from mechanical fufpenfion. Fofiils having foliated, radiated, or fibrous frac tures, are molt unqueftionably. formed by preci pitation from a ftate of chemical folution. Nearly all fofiils having a conchoidal or uneven fraCture, a ftrong luftre, tranflucency, even only tranflucen- cy on the edges, are in general products from chemical folution. On the contrary, fofiils the produCt of mechanical depofition, are opaque, friable, dull, earthy, and fometimes alfo fome- what indurated. We frequently obferve, inter mixed with this mechanical depofit, foreign par ticles that are either fragments or rolled pieces. In