After the retreat of the last of the great ice sheets from Illinois,
numerous ponds and lakes were left in northern Illinois, especially in
the eastern section. Some of them were soon drained by natural
processes, but others remained. In the shallow water along their shores
grew various plants, chiefly reeds and sedges and, locally, a variety of
moss. As the plants died, their partially decomposed remains were
preserved beneath the water. Ultimately, the ponds and lakes were
overgrown and more or less completely filled by the plants and their
remains, giving rise to peat (fig. 22) bogs.
Some peat bogs have been drained and are now used as farm land. Others
remain and a few of them are the source of peat or humus for
horticultural purposes. Producing operations are located in northeastern
Illinois and in Whiteside County in northwestern Illinois.