4.2 Microbial Mats, Stromatolites and Their Environments .............................................. 67 4.2.1 What Are Microbial Mats and Stromatolites? Some De fi nitions ...................................................................... 67 4.2.2 Microbial Mats and Stromatolites: The Geological Evidence ............................................... 67 4.2.3 Strati fi cation and Struct...