Pollen grains, because of their wide dispersal, are excellent fossils and are commonly preserved in lake muds. Much of the Atherton Tableland consists of lava erupted during the last 3 million years. On the Tableland are several volcanic craters, the ends of pipes from which gases, rock fragments and lava were ejected. Some of these craters are edged by well defined ridges and contain lakes. Barrine, Eacham, Quincan and Euramoo are good examples.
Crater lakes are excellent sites for pollen analysis.
Material washed into a lake sinks and is deposited in the mud on the bottom. In deep, still lakes the mud, once deposited, remains undisturbed. Mud accumulates year by year, that being deposited in any one year falling on top of the mud in previous years. The youngest mud is that being laid down now at the top of the mud column. The change in composition of mud from its surface can itself yield important information about environmental change such as soil erosion or chemical pollution.