Clay Slate. Obfervations. 1. It is to bs obferved paffing intofeveral congene- r °us foffils j thus the oldeft primitive clay flate has a confiderable degree of luftre, (hews a beginning fcaly afpefl:, and pafies ‘into mica flate ; the greenifh va- Tieties, by an increafe of their proportion of magne- fian earth, and confequent alteration of external cha racters, pafs into whet flate, chorite flate, and indu rated talc. It may even pafs into flate clay, but I do Rot know that this has ever been obferved. 2. In places where the fplintery variety is found, the feparated malfes appear like rotten wood. TWENTY-