Sodium is present primarily as exchangeable cations in lignite, and its concentration is inversely proportional to calcium cations. The presence and concentration of the calcium cations in lignite appear to be related to the calcium ion concentration and permeability of the immediate roof rock, sandstones or glacial drift. Data obtained from several hundred bore holes and field checks in strip mines indicate that there is a good correlation between low sodium content in lignite and the presence of sandy roof rocks.