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37° Derivatives. S E C T I O N XII. Of Mixed Earths, and Derivative Stones. With Supplemental Obfervations. Earths, refulting from the union of earths, or fands, are called mixed, becaufe the ingredients united are, at leaft for the moft part, vifibly diftinö, and may in great meafure be mechani- cally feparated. Stones, refulting from the coalition of ftones of different fpecies, are called derivatives; they dif- fer from aggregates in this, that the affociated ingredients are not vilibly diftindl, or, at leaft, require microlcopes to render them fo. The co- alefcingy/&«ei may differ either by their ingredients, when both are compofed of many, or by the pro- portion of fome ingredient or ingredients com mon to both fpecies. If the coaleicing fpecies differ by one or tnore ingredients, the coalition is formed by the addition of thefe, or lome of them, to the fpecies that had them not, or by their fubtra&ion from the fpecies that had them. So alfo, if the coalefcing fpecies differ in the proportion of their ingredients, the coalition »s formed by augmenting that proportion in the one, and leflening it in the other.