Huttonian Theory* 345 of unqueftionable ingenuity, but very imperfe&ly {killed in mineralogy, inferred, from his obferva- tions, that theprefent world has been formed from the debris of two former worlds, inhabited by nu merous tribes of animals, and clothed with a pro- fufion of the moft magnificent vegetables. Ac cording to this ftrange hypothefis, even gneifs, mica-fiate and clay-flate are but mechanical depo- fites, which have been foftened by the a£tion of heat, fo as to permit their being elevated, with out breaking, from their fuppoled original horizon tal pofition, to their prefent vertical one. It is admitted by all geognofts, except the Hut- tonians, that there exifts a great clafs of rocks, denominated Primitive, which forms the oldeft part of the earth, and contains no materials more ancient than itfelf, but is a true chemical depo- fition; confequently that this world cannot be confidcred as deriving any of its materials from onef or more worlds antecedent to it. If the truth of this faft can be eftablilhed, it is evident, that the Huttonian Theory, notwithftanding the power ful eloquence ufed in its fupport, muft be reje&ed as groundlefs. As Gneifs and Mica-llate are part of this primi tive feries, and are confidered by the Huttonians to be the oldeft rocks at prefent known ; let us inquire, if there be any evidence in favour of the fuppofition that they are mechanical depofites. Thefe two rocks, like granite, have a granular Vol. HI. X x ftrufture.