Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/257

 Rh which they are found, and vary in size from a line to more than four feet in diameter.

It is needless here to speculate either on the physical, or final causes which produced these curious changes of species, in this highest order of the Molluscous inhabitants of the seas, during some of the early and the middle ages of geological chronology; but the exquisite symmetry, beauty, and minute delicacy of structure, that pervade each variation of contrivance throughout several hundred species, leave no room to doubt the exercise of Design and Intelligence in their construction; although we cannot always