intersected by another set of drifts about forty feet apart, ruuning.at right angles with them, and of course parallel with the main abaft or " incline." Thus tho whole bod of oaal i* eat through with passages crossing one another, leaving large masses of coal, called " pillars," to support the roof. When tho whoa* seam is thus explored, and the drifts have struck rock ail around, then commences the work of " robbing"—cutting away the