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Of the Formation of Stones. 21 Some fubftances are more apt to be dlfturbed by the introdu&ion of foreign fubftances than others; thus we fee calcareous fpars cryftailized in a regulär form, though mixed with a confide- rable proportion of filex, in the calcareous fand- ftones of Fontainbleau. The firft ftep in the procefs of cryftallization is the formation of grains, the fecond is the increafe in one dimenfion, the third in two dimenfions, and the fourth in three dimenfions; the grains them- felves, however, to be vifible, muft receive ac- cretions in the three dimenfions. lf the procefs be uninterrupted, no traces of diftintftion will be perceived, and the whole will appear perfedfly uniform; but, if it be difturbed in the firft ftep, no cryftallization can take place; if in the fecond, the grains will appear diftindt, fmall or grofs, coarfe or fine, according to the nature of the difturbance, whether by the interruption of the procefs, or the acceffion of foreign matter; s * a _ tt er generally produces coarfe or rude grains in proportion to the quantity. If the difturbance only takes place in the third ftage, we fhall have fibres or ftri®, as complete lurfaces cannot be formed; the ftriffi, having more extenfion in breadth than the fibres or filaments, argue a fmaller degree of difturbance than the mere fibrous appearance. . If, during the third ftage, the ftrije be forced mto contaft, by the gradual dereliftion of the U1 kept them fufpended, they will form Jamella m proportion as they aredeferted, which will either adhere to each other, and then fall confufedly, being too heavy to be fupported by the menftruum, or, if fupported, will be fuper- lmpofed 011 each other. l C 3 But