Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/260

 256 was analogous to that of the inhabitant of the Nautilus Pompilius. (See Pl. 31, Fig. 1.)

Mr. De la Beche has shown that the mineral condition of the outer chamber of many Ammonites, from the Lias at Lyme Regis, proves that the entire body was contained within it; and that these animals were suddenly destroyed and buried in the earthy sediment of which the lias is composed, before their bodies had either undergone decay, or been devoured by the crustaceous Carnivora with which the bottom of the sea then abounded.

As all these shells served the double office of affording protection, and acting as floats, it was necessary that they should be thin, or they would have been too heavy to rise to the surface: it was not less necessary that they should be strong, to resist pressure at the bottom of the sea; and accordingly we find them fitted for this double function, by the disposition of their materials, in a manner calculated to combine lightness and buoyancy with strength.