in natural history, a hard, and as it were stony covering, with which certain animals are defended, and thence called shell-fish.

As to the formation of a shell, it is now generally allowed to be formed by a viscous fluid composed of glue, and several sandy particles of an exquisite fineness, which are transmitted through an infinite number of little channels to the pores where it transpires, condenses, and hardens. When the animal increases in bulk, and the extremity of her body is not sufficiently covered, it continues to evacuate and build in the same manner, finishing or repairing her habitation. This viscous matter is proved, by undeniable experiments, to arise from the body of animals, and not from the shell, as some have imagined.

FOSSIL SHELLS, those found buried at great depths in earth, and often immersed in the hardest stones. These fossil shells, as well as those found lying on the sea-shore, make an excellent manure, especially for cold clayey lands; upon which it does not produce nearly so great an effect for the two first years, as it does in the succeeding ones; the reason of which is, that it is not then sufficiently mixed, but in succeeding time it breaks itself into a number of very small particles, and these all become intimately blended with the molecules of earth, and produce their effect more properly.