Tropical lakes, copropel, and oil shale
During a long-continued study of the lacustrine beds of the Eocene Green River Formation, an attempt was made to interpret past events from observation of present-day processes. After a search of some 40 years, four lakes have been found that are producing a kind of organic ooze judged to be a modern analogue of the precursors of rich oil shale. Two of the lakes are in central Africa and two are in Florida. All four are shallow. The ooze in all four is predominantly algal, entirely in the form of minute fecal pellets, and does not decay in warm, wet, oxidizing environments. Several of the most unusual, mummified microorganisms found in the oil shale of the Green River are illustrated as testament to the inference that the organic oozes also were resistant to decay. Studies to determine why these algal oozes do not decay are in progress, but as yet no satisfactory explanation is available.