To assist in locating the best site for the Lake Vanda drill hole, the nature of the bottom surface sediments was studied for the purpose of constructing a general bathymetric map of the lake. A maximum depth of 68.6 m is recorded near the center of the western lobe of the lake. Lake bottom sediments sampled at 25 drill holes show two contrasting bottom sediment facies. Shallower than 60 m the environment is aerobic, consisting mainly of pale fawn and quartzofeldspathic sands, overlain by a layer of biological detritus containing algae, diatoms, fungal mycelia, bacteria, and terrigenous sand. Below 60 m the environment is anaerobic, the sediments consisting of sandy muds and muddy sands rich in finely disseminated organic matter. The bathymetric map is shown