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IOO PRIMITIVE ROCKS. Class IV. Alluvial Rocks. 1. Peat. ^ Nagelfluh. 2. Sand and Gravel. 6. Calc-tuff. 3- Loam - 7. Calc-finter. 4- Bog Iron-ore. Class V. Volcanic Rocks. * Pfeudo-Volcanic Rocks. 1. Burnt-CIay. 4. Columnar Clay-Ironftone, 2. Porcelain-Jafper. 5. Polier, or Polifliing Slate. 3. Earth-Slag. ** True Volcanic Rocks. 1. Ejected Stones and Allies. 3. The matter of Muddy 2. Different kinds of Lava. Eruptions. CHAP. VI. Class I.—Primitive-Rocks. Urgebirge.—Werner. 4 8 - ’THE rocks belonging to this clafs are the ol- X deft parts of the cruft of the globe. They are principally cotnpofed of liliceous and argillaceous earths: magnefian earth alfo occurs, but princi pally in the newer rocks of this clafs. When they occur with any of the other four clafles of rocks,