Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/265

 Rh

At Pl. 35, from d. to e. we see the edges of the same transverse plates which, in Pl. 36, are simple curves, becoming foliated at their junction with the outer shell, and thus distributing their support more equally beneath all its parts, than if these simple curves had been continued to the extremity of the transverse plates. In more than two hundred known species of Ammonites, the transverse plates present some beautifully varied modifications of this foliated expansion at their edges; the effect of which, in every case, is to increase the strength of the outer shell, by multiplying the subjacent points of resistance to external pressure. We know that the pressure of the sea, at no great depth, will force a cork into a bottle filled with air, or crush a hollow cylinder or sphere of thin copper; and as the air chambers of Ammonites were subject to similar pressure, whilst at the bottom of the sea, they required some peculiar provision to preserve them from destruction, more especially as most zoologists agree that they existed at great depths, "dans les grandes profondeurs des mers."