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68 INTERNAL STRUCTURE. Granite, Gneifs, Mi’ca-flate, Clay-flate, Serpentine, Porphyry, and Sienite, are of this kind. Of thefe Granite is the oldeft, and Sienite the neweft. To this fucceeds another confiderable clafs of rocks, which Werner denominates tranfition. In this clafs, which is principally compofed of chemical produ&ions, mechanical depofitions firft make their appearance, but in the earlier part ia inconfiderable quantity. Limeftone firft occurs in confiderable quantity in this clafs. Grey-wacke, Grey-wacke Slate, and Tranfition Limeftone, are the predominating rocks of this clafs. Still newer, and confequently lower, than the tranfition clafs, is the extenfive clafs of Flcetz Rocks. •Here mechanical depofits occur in great quantity, and the proportion of chemical precipitate de- creafes. The principal rocks are Limeftone and Sandftone : to thefe may be added, Gypfum, Salt, and great accumulations of inflammable matter in 'the ftate of Coal. 1 Still newer and lower is the clafs of Alluvial Rocks, which are almoft entirely compofed of me chanical depofits. Sand, Clay, Loam, and Coal, , are the principal earthy mafles that belong to this clafs. The neweft of all, is the clafs of Volcanic Rocks, Different kinds of Lava and Tuff include nearly all the variety of rocks belonging to this clafs. A