Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 2.djvu/69

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across the cavities of the Air chambers. As in the recent Nautilus Pompilius, there is no communication between the interior of the Siphon and that of the Air chambers, so in this fossil shell, there is proof that no communication existed between these cavities. A transverse section at a. shows the thin edge of the sheath of the siphuncle, surrounded externally with calcareous spar, and filled internally with Grit. Other Sections of the Siphuncle at b. d. e. f. show the calcareous Grit within its cavities to be contracted at its passage through the collars of the transverse plates, and most enlarged midway between one transverse plate and another.

This fossil affords two proofs that no communication existed between the interior of the Siphuncle and that of the Air chambers. 1st. the calcareous sheath of the Siphuncle is seen at d. e. f. completely enclosing the calcareous grit which forms the cast within it. 2dly, had there been any communication between the interior of the siphuncle, and that of the air chambers, these chambers must have received some portion of the materials of the grit that have filled this Siphuncle: not a particle of grit is found in any one of the adjacent air chambers, but they are all lined, and some of them nearly filled with a crystalline deposite of Carbonate of Lime, disposed in uniform plates around the interior of each chamber, and around the Siphuncle. See Fig. 2. c. c 1. a. a1, a2, a3, and Fig. 3. d—k. This deposite can only have been formed from water charged with carbonate of lime, introduced by infiltration, after the interment of the shell, and filling the chambers which are thus uniformly invested.