cyanobacterium mats, with fieldwork along the Red Sea coast. The fieldwork never materialised but my interest in algal mats had been aroused. A chance stroll along the Bangor shore revealed beautifully calcified cya- bacterium mats, and Tony generously allowed me to investigate these instead. The old Plaxtol collection was retrieved and yielded abundant cyanobacteria. It became apparent that here was a wealth of information about a rock whose formation was so rapid, that the process could be studied in days rather than years - an exceptional state of affairs. A search of the literature also revealed that the rock, a form of travertine, had other unusual features.