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Eßfall. 447 fagacity in tracing, cryftalüne forms are acknow- ledged, though he at firft admitted bafaks among them, yet, in his Second Edition, on mature con- fideration, he basoxcluded them: “ thde cryi- “ talliform mafles (fays he) are always the pro- ££ dufts, not of a true crvftallization, but of a t£ heterogeneous matter, not difTolved, but pre- £ ‘ cipitated undcr an irregulär form, and alter- £t wards, eithcr by deficcarion or cooling, burft “ or conrracicd inro prilhis of a greatcr or Iciler ££ nuinber of fides, but idways iudeterminate. “ ln vain fhould one feek in t liefe p:ercnded_cryf- ££ tals, ciiiura conftant paralblHm of ftie planes, “ or a determinate meafuve in tue angles, c>:-c.” x Cryftal'.ogr. p. 439- , . , ßeiidrs, ic is weil known, that r.o fuMlancc can cryftallizc eithcr in a mtnüruum, or iioni a folution by heat, unlef, k bc lb pcrloftiy difioived that its parts have liberty to a : 'rar.ge themlelves according to their pcculiav a< traaions •, io that, if they crylfnllize irom a ftate of fufton, nie iuhon muff have been thin and pirieft : tiow it is evi dent, froni fuch fufton, glafs or enamfts muß be formed, unlcls the mutt luiible paris bc diflipated. or fepurated ; vvhich is not the cafe in batabs, fince in rheir aftual ftate they arc eafily and per- feftiy fufible, fo that we have herein a deinon- ftration, a prien, that they are not formed by cryllailization in the dry way. Again, bafalts are frequent ly found on tue fummits of mountains; how then can thcii foi- niation bc confined to internal^ cavitics ? Mr. Defmarerz found them on the iummirs of Puy de Befclle, Puy de Trcuil, Puys d’Iir.igncs, Puy de Mazeircs, 8tc. in Auvergne; Mr. fialck 011 that of Cottencr, near Kteniglkin, in.Mifnia; ivir.