CALC GENUS. It is employed in improving bad land; as mortar ; and when Iimeftone is not to be found, in the fmehl’ ing of certain ores of iron. Obfervatiom. r. It falls in the air. 2. It pafles into limeflone and indurated clay, which latter I fufpeft has been confounded by I)r. Reufs^with bafalt, when he fpeaks of marie paffintr into bafalt. 3. According as alumina or filica preponderates, it receives the name of clay cr lime marie- Hauy be lieves it to be a mechanical mixture, and fays it ihonld not be confidered as a mineral fpecies. To the eye, however, it has every charader of a Ample fcffil, therefore it is entitled to a place in a fyflem of oryctognofie. t 3 Y 2 ELEVENTH