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 but whose origin and formation have never yet been fully explained. I shall not enter into a minute detail of the several species of the Belemnite. The history of this extraneous fossil, or an attempt to account for the origin and formation of the Belemnite, so far as they can be discovered and confirmed by reasonings drawn from facts and experience, is the object of the present enquiry. I shall therefore confine my self to two species of the Belemnite; the one common in most counties of this kingdom, and vulgarly known by the name of Thunder-bolt : the other that of the fusiform or Spindlekind, found in slate-stone at Stons-field, but in far greater plenty in the clay near Piddington Oxfordshire; and in the chalk-pits of Kent and Surrey. Those in chalk have been often mistaken for spines of the tea-hedgehog, or Echinus Ovarius; but the characteristics of these two bodies are widely different. The Belemnite breaks in a direction perpendicular to its axis : the spine obliquely. The Belemnite, when broken, exhibits central rays; the Spine a smooth resplendent surface. This distinction is invariable, if the trial be repeated a thousand times. These differerent appearances are probably the effects of different formations: and therefore the Belemnite seems to be formed by apposition, and the Aculcus or Spine by protrusion, or, as Mr. Reaumur calls it, by intus-susception. The radii in the Belemnite are owing to the fine laminæ, of which it is composed; they are so very thin, and break to nearly alike, that they have ever an horizontal surface when broken,

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