350 On M. Humboldt’s Theory of Rocks. Note[IIL.] In examining his " tabular arrangement” merely as a matter of fact, we are particularly beholden to him for the ingenious and beautiful scheme which he has devised for bringing the whole of it within the easy grasp of the discernment, by his " pasigraphic or algorithmic method “ of indicating the superposition of rocks, as the terms of “ a series; — by which we may, by means of twelve geo- “ gnostic signs, exhibit the most important phenomena “ of position of the primitive, intermediary, secondary, “ and tertiary (or upper-secondary) formations 1 .” I shall not withhold this method from my reader. " To designate the four most ancient primitive forma- “ tions, M. Humboldt employs the first four letters of the " Greek alphabet, a, [3, y, 8these, for a reason which will appear, I shall place in capital characters: " A—g r ^nite. “ B—gneiss. " r—mica-slate. “ A — clay-slate. For all the remaining formations, he takes the initial letter of a Greek word significative of them, respectively, e.g. " <>■—(opg) serpentine, and every formation abound ing in diallage. a— (Zunvn) syenite, and every formation abounding in hornblende. “ T—porphyry; which sometimes passes to «(syenite), and sometimes to o (serpentine). T—(riravoi) calcareous formations. r •—'primitive limestone. r —limestone with organic remains. r 1 — transition limestone.
