19+ flint genus. 3. It is often confounded with green opal, front which it differs, however, in fradure, luftre, hard- nefs and weight. 4. May not chryfopras, plafma, and heliotrope, as well Hand under chalcedony, as milk quartz and prafe under quartz ? 5. Very elegant fpecimens of this beautiful foflil are to be feen in the great cathedral at Prague, where a clofet is inlaid with it. , TWENTY-NINTH SPECIES. Flinty Slate. Kiefelfchiefer.—Werner. This fpecies is by Werner divided into two fub* fpecies. 1. Common flinty flate. 2. Lydian ftone. FIRST