The sediments covering the bottom of Devils Lake below the depth of about six meters are fine muds. Above six meters they increase in coarseness with decrease in depth to become sands or courser materials on the shores. The immediate bottom of the lake at short distances from the shores is covered with a black soupy liquid that is termed sludge. This has a maximum thickness estimated as about one meter. The sediments beneath the sludge are black and have an average water content of 82.5 per cent. Silicon dioxide is the chief constituent of the inorganic part of the sediments and ranges in percentage between 50 to more than 60 per cent. There is little or no calcium or magnesium carbonate, The organic content of the sediments is estimated to be between 15 and 20 per cent. Bacteria are not particularly abundant in the muds beneath the sludge, but aerobic and facultative bacteria average over a million per gram of dry sludge.