Bricks. - An important discovery has lately been made by Mr. Whitmore Davis, at Castle Comber, in the county of Kilkenny, Ireland. He observed some persons in the vicinity of a colliery, to employ a mortar for the backs of their grates, which in a short time became hard. This substance he found, on examination, to be what miners term seat-coal, or that fossil which lies between coal and the rock. It has been submitted to the investigation of Mr. Kirwan, who is of opinion, that it will, when mixed in due proportions with clay, produce a kind of bricks, capable of resisting the action of fire, and consequently well calculated for furnaces, or similar structures. Mr. Davis has accordingly employed it with success ; and he farther observes, that seat-coal, if properly prepared, will answer every purpose of tarras, for buildings beneath water.