an old term in Natural History; applied to spars debased by a very large admixture of earth: they are opaque, formed of thin crusts, covering vegetables and other bodies, by way of incrustations.

Of this genus we have the following species; 1. A grayish white one, with a rough surface. 2. A whitish brown one; both these are friable. 3. A hard, pale brown kind, which is the osteocolla of the shops. 4. The whitish-gray kind, with a smooth surface: this is the unicorn fossil and ceratites of authors. 5. The whitish brown coraloid kind.